Put conf_file loop outside of init_file loop

[thalesmello]

Addreses #665

[scorphus]

LGTM

Thanks, @thalesmello

[derekstavis]

Thanks for taking the time to debug and fix this bug!

The loop was done on purpose. As you can see, globs are used thoroughly in require function, and it is used mainly because it is a performant way of checking for the existence of one or more files without forking to a subprocess or calling test (which is prohibitive in the init code path).

The $init_path variable in this case is populated with all init.fish files present in package directory, which should return one and only one file (yes, prepending anything after .fish will give bogus stuff). Further in the code, if the given init.fish file was already sourced, we skip loading again, what would avoid reloading conf.d twice.

I noticed that this PR fixes another bug that I didn't notice when adding conf.d loading! Currently conf.d is only being loaded when init.fish is present, which is not what we wanted to achieve.

I'm not gonna block the merge, but I will leave some concerns that we might want to address in the future:

1. The mechanism that will not source init.fish (or init files, which includes conf.d) is not effective for conf.d anymore (https://github.com/oh-my-fish/oh-my-fish/blob/master/lib/require.fish#L55)
2. The benchmarking events will not take conf.d into account anymore (https://github.com/oh-my-fish/oh-my-fish/blob/master/lib/require.fish#L84)