Allow failures from single-file globs

[ghost]

If you stage a file and then delete it, git ls-files will still include that file. However, because this is using the default glob settings, it will fail for single-file globs. If this behaviour is kept, it should at least catch the exception and print a nicer error.

IMHO this behaviour should be disabled on default, but I'd settle for a flag if that's desired too.