Revert "Remove redundant music checks in frontend methods"

[Geokureli]

Reverts #3586

This is a breaking change. It breaks any project that manually replaces FlxG.sound.music, most notably Funkin'.

From what I've gathered, FlxG.sound.music used to be updated independently of the sound list. If you wanted to replace it with a custom sound you could simply reassign it (and remove it from the sound list, if created via FlxG.sound). (example)

Since it's no longer updated independently, projects that do the aforementioned now have music that doesn't update, which is especially problematic in FNF's case as the sound time no longer updates, and therefore the gameplay gets stuck

[moxie-coder]

I'm guessing this broke something?

[ACrazyTown]

I'm guessing this broke something?

#3586 (comment)