Commandline: Flatten and refactor getCompatData

[sonic2kk]

Along the lines of #1031 and #1011, but also a slightly more significant refactor.

This PR flattens the structure of getCompatData , making it return early instead of having a bunch of nesting. It also removes an unnecessary codepath. We had some weird check for STLCOMPDAT existing and we would error out if it didn't. This was probably a holdover from the time when this function relied entirely on STLCOMPDAT to parse symlinks. We no longer do this. Instead, this check now wraps our symlink check. So we only check STLCOMPDAT for symlinks if it exists, and if we find a path to the compatdata we're looking for, we return it here and exit early. This makes much more logical sense to me; if we didn't find the path in STLCOMPDAT we were moving on to check for the compatdata in the library folder manually anyway, so there's no need to error out if the STL folder simply doesn't exist (which is almost guaranteed to never be the case as STL verifies its folder structure).

STLCOMPDAT just points to, for example, ~/.config/steamtinkerlaunch/compatdata. It doesn't represent any specific compdatdata, so this check was a pointless check on the STL folder structure. There is no need to error out. Honestly, the -d check is kind of pointless to begin with, but it's for safety in case find gives us unexpected results if -d is not a valid directory.

Apart from that, it's just flattening the logic to remove nesting.

[sonic2kk]

Needs a rebase and some more testing, but ShellCheck is green.

[sonic2kk]

Appears to work in testing, can probably rebase and merge.

[sonic2kk]

ShellCheck is green still after a rebase and this seems to work fine, can merge.