crash when boundry alignment is on

Hello,
Windows 10
MSYS2/Mingw toolchain

Steps to reproduce
1. ./fieldviz.exe data/bunny.obj
2. Press space
3. press b (boundry alignment now on)
4. press space

program crashes with error:
```
Assertion failed: abs( s - lround( s ) ) < 1e-6, file src/KVecDir.cpp, line 472
```