Crash on completition - Unicode boundary bug

[colonelx]

It breaks on Cyrillic letters. Error: end of range should be a character boundary

Reason

Cyrillic characters in UTF-8 are encoded using 2 bytes per character.

locale:

LANG=bg_BG.UTF-8
LC_CTYPE="bg_BG.UTF-8"
LC_NUMERIC="bg_BG.UTF-8"
LC_TIME="bg_BG.UTF-8"
LC_COLLATE="bg_BG.UTF-8"
LC_MONETARY="bg_BG.UTF-8"
LC_MESSAGES="bg_BG.UTF-8"
LC_PAPER="bg_BG.UTF-8"
LC_NAME="bg_BG.UTF-8"
LC_ADDRESS="bg_BG.UTF-8"
LC_TELEPHONE="bg_BG.UTF-8"
LC_MEASUREMENT="bg_BG.UTF-8"
LC_IDENTIFICATION="bg_BG.UTF-8"
LC_ALL=

Log

 �[1m[�[31mERROR�[0m	]�[0m �[36msrc/main.rs�[0m: panicked at src/bash_server.rs:26:33:
called `Result::unwrap()` on an `Err` value: RecvError
�[1m[�[31mERROR�[0m	]�[0m �[36msrc/main.rs�[0m: panicked at src/mainloop.rs:1008:20:
end of range should be a character boundary
�[1m[�[31mERROR�[0m	]�[0m �[36msrc/main.rs�[0m:    0:     0x55eb1a5ba4df - backtrace[f094e2566e6eba7b]::backtrace::libunwind::trace
                               at /data/viktor/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/backtrace-0.3.66/src/backtrace/libunwind.rs:93:5
                           backtrace[f094e2566e6eba7b]::backtrace::trace_unsynchronized::<<backtrace[f094e2566e6eba7b]::capture::Backtrace>::create::{closure#0}>
                               at /data/viktor/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/backtrace-0.3.66/src/backtrace/mod.rs:66:5
                           backtrace[f094e2566e6eba7b]::backtrace::trace::<<backtrace[f094e2566e6eba7b]::capture::Backtrace>::create::{closure#0}>
                               at /data/viktor/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/backtrace-0.3.66/src/backtrace/mod.rs:53:14
                           <backtrace[f094e2566e6eba7b]::capture::Backtrace>::create
                               at /data/viktor/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/backtrace-0.3.66/src/capture.rs:176:9
                           <backtrace[f094e2566e6eba7b]::capture::Backtrace>::new
                               at /data/viktor/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/backtrace-0.3.66/src/capture.rs:140:22
   1:     0x55eb1a53dd9d - nsh[4697820c212381d0]::main::{closure#0}
                               at /usr/src/debug/nsh-git/nsh/src/main.rs:187:25
   2:     0x55eb1a644ddf - <alloc[d7a0dcdcba99736a]::boxed::Box<dyn for<'a, 'b> core[94ad8b403119b81d]::ops::function::Fn<(&'a std[151076651bcecd14]::panic::PanicHookInfo<'b>,), Output = ()> + core[94ad8b403119b81d]::marker::Send + core[94ad8b403119b81d]::marker::Sync> as core[94ad8b403119b81d]::ops::function::Fn<(&std[151076651bcecd14]::panic::PanicHookInfo,)>>::call
                               at /rustc/9e79395f92bff6a8f536430e42a4beae69f60ff8/library/alloc/src/boxed.rs:2220:9
                           std[151076651bcecd14]::panicking::panic_with_hook
                               at /rustc/9e79395f92bff6a8f536430e42a4beae69f60ff8/library/std/src/panicking.rs:833:13
   3:     0x55eb1a66d608 - std[151076651bcecd14]::panicking::panic_handler::{closure#0}
                               at /rustc/9e79395f92bff6a8f536430e42a4beae69f60ff8/library/std/src/panicking.rs:691:13
   4:     0x55eb1a66d589 - std[151076651bcecd14]::sys::backtrace::__rust_end_short_backtrace::<std[151076651bcecd14]::panicking::panic_handler::{closure#0}, !>
                               at /rustc/9e79395f92bff6a8f536430e42a4beae69f60ff8/library/std/src/sys/backtrace.rs:182:18
   5:     0x55eb1a66db2c - __rustc[fb814a8b796c654f]::rust_begin_unwind
                               at /rustc/9e79395f92bff6a8f536430e42a4beae69f60ff8/library/std/src/panicking.rs:689:5
   6:     0x55eb1a60b13b - core[94ad8b403119b81d]::panicking::panic_fmt
                               at /rustc/9e79395f92bff6a8f536430e42a4beae69f60ff8/library/core/src/panicking.rs:80:14
   7:     0x55eb1a571d08 - <alloc[d7a0dcdcba99736a]::string::String>::replace_range::<core[94ad8b403119b81d]::ops::range::Range<usize>>
                               at /rustc/9e79395f92bff6a8f536430e42a4beae69f60ff8/library/alloc/src/string.rs:2086:9
                           <nsh[4697820c212381d0]::mainloop::UserInput>::replace_range
                               at /usr/src/debug/nsh-git/nsh/src/mainloop.rs:1008:20
                           <nsh[4697820c212381d0]::mainloop::Mainloop>::select_completion
                               at /usr/src/debug/nsh-git/nsh/src/mainloop.rs:722:28
   8:     0x55eb1a5738d6 - <nsh[4697820c212381d0]::mainloop::Mainloop>::update_completion_entries
                               at /usr/src/debug/nsh-git/nsh/src/mainloop.rs:686:18
   9:     0x55eb1a56cdc1 - <nsh[4697820c212381d0]::mainloop::Mainloop>::handle_event
                               at /usr/src/debug/nsh-git/nsh/src/mainloop.rs:283:22
  10:     0x55eb1a54adaf - <nsh[4697820c212381d0]::mainloop::Mainloop>::run
                               at /usr/src/debug/nsh-git/nsh/src/mainloop.rs:170:30
                           nsh[4697820c212381d0]::interactive_mode
                               at /usr/src/debug/nsh-git/nsh/src/main.rs:68:36
  11:     0x55eb1a54e8b3 - nsh[4697820c212381d0]::shell_main
                               at /usr/src/debug/nsh-git/nsh/src/main.rs:122:13
                           nsh[4697820c212381d0]::main
                               at /usr/src/debug/nsh-git/nsh/src/main.rs:200:5
  12:     0x55eb1a52b1e6 - <fn() as core[94ad8b403119b81d]::ops::function::FnOnce<()>>::call_once
                               at /rustc/9e79395f92bff6a8f536430e42a4beae69f60ff8/library/core/src/ops/function.rs:250:5
                           std[151076651bcecd14]::sys::backtrace::__rust_begin_short_backtrace::<fn(), ()>
                               at /rustc/9e79395f92bff6a8f536430e42a4beae69f60ff8/library/std/src/sys/backtrace.rs:166:18
  13:     0x55eb1a5b0579 - main
  14:     0x7fcc6a9d26c1 - <unknown>
  15:     0x7fcc6a9d27f9 - __libc_start_main
  16:     0x55eb1a4fd2f5 - _start
  17:                0x0 - <unknown>
 �[1m[�[31mERROR�[0m	]�[0m �[36msrc/main.rs�[0m: panicked at src/bash_server.rs:26:33:
called `Result::unwrap()` on an `Err` value: RecvError

Steps to reproduce:

1. Create folder named "Свалени"
2. Type: ls Сва
3. Press Tab
4. nsh panics