ghq(1) gets panic if current working directory is removed

[gfx]

I have reported it here for information, but I expect that it is a kind of "wontfix" issue because it occurs in an abnormal environment.

Env

• ghq 0.8.0 installed via homebrew

How to reproduce

1. Open two terminals with the same cwd
2. Runmkdir foo in one terminal
3. Run rmdir foo in another terminal
4. Run ghq root in the first terminal

output:

fatal: Unable to read current working directory: No such file or directory
panic: exit status 128

goroutine 1 [running]:
github.com/motemen/ghq/utils.PanicIf(0x124f700, 0xc42008ad80)
	/private/tmp/ghq-20170822-8571-7p2dyy/ghq-0.8.0/src/github.com/motemen/ghq/utils/log.go:53 +0x4a
main.localRepositoryRoots(0x3, 0xc42006c660, 0x119b600)
	/private/tmp/ghq-20170822-8571-7p2dyy/ghq-0.8.0/local_repository.go:195 +0x485
main.primaryLocalRepositoryRoot(0xc4200906e0, 0x119b2b8)
	/private/tmp/ghq-20170822-8571-7p2dyy/ghq-0.8.0/local_repository.go:219 +0x22
main.doRoot(0xc4200906e0, 0x0, 0xc4200906e0)
	/private/tmp/ghq-20170822-8571-7p2dyy/ghq-0.8.0/commands.go:453 +0x158
github.com/urfave/cli.HandleAction(0x116ab00, 0x11a5c98, 0xc4200906e0, 0xc42006c600, 0x0)
	/private/tmp/ghq-20170822-8571-7p2dyy/ghq-0.8.0/src/github.com/urfave/cli/app.go:490 +0xd4
github.com/urfave/cli.Command.Run(0x119b4e1, 0x4, 0x0, 0x0, 0x0, 0x0, 0x0, 0x119f53e, 0x17, 0x0, ...)
	/private/tmp/ghq-20170822-8571-7p2dyy/ghq-0.8.0/src/github.com/urfave/cli/command.go:210 +0xb6e
github.com/urfave/cli.(*App).Run(0xc420052ea0, 0xc42008a080, 0x2, 0x2, 0x0, 0x0)
	/private/tmp/ghq-20170822-8571-7p2dyy/ghq-0.8.0/src/github.com/urfave/cli/app.go:255 +0x76f
main.main()
	/private/tmp/ghq-20170822-8571-7p2dyy/ghq-0.8.0/main.go:12 +0x53