todo panics when executing Get on /todo/all window

[lufia]

steps to reproduce

1. open Acme editor
2. execute todo -a
3. execute Get on tag line of /todo/all window

panic: interface conversion: interface is nil, not error

goroutine 6 [running]:
9fans.net/go/acme.(*Win).execute(0xc0000f6000, 0x1245ca0, 0xc0000a0060, 0xc0000947c0, 0x3, 0x3)
	/Users/lufia/pkg/mod/9fans.net/go@v0.0.1/acme/acme.go:864 +0x496
9fans.net/go/acme.(*Win).EventLoop(0xc0000f6000, 0x1245ca0, 0xc0000a0060)
	/Users/lufia/pkg/mod/9fans.net/go@v0.0.1/acme/acme.go:796 +0x103
created by main.open
	/Users/lufia/pkg/mod/rsc.io/todo@v0.0.2/acme.go:110 +0x373

This looks like issue of 9fans.net/go/acme.
https://play.golang.org/p/kutgsDd4-eT

[benghancock]

Hi @rsc - Thanks for this handy tool! I still experience this issue when executing Get in the /todo/all window in Acme, though it appears the underlying fix has been applied upstream. Bumping the version as suggested in PR #3 resolved the issue for me.