Adjust parser ordering to error out on invalid names
Adjust parser ordering to error out on invalid names

See https://github.com/tianon/gosu/commit/fd60171def742cc35f31e2076bc24c4b94b422c9 and https://github.com/tianon/gosu/commit/f87df69c868e19f7258b4facb7c2472d76d98dda.

The basic problem is that an invalid name like `bogus` will quietly run as `root` instead of being denied entirely (which those test updates look for and this change is verified to fix).

I've run this updated implementation successfully against all of the test cases in https://github.com/tianon/gosu/blob/f87df69c868e19f7258b4facb7c2472d76d98dda/Dockerfile.test.

ncopa/su-exec