[BUG][PLAYER] If music file is missing, last level's music is played instead.

[namida]

Steps to reproduce:

1. Play a level that has music - I don't know if it has to be outright specified, or if a level that uses normal rotation will work.
2. Play a level that has no music specified (including that the standard rotation for that pack should be blank), or specifies a music file that doesn't exist.

Expected: No music plays. In the case of a file that doesn't exist, possibly a warning message pops up - perhaps only the first time that level is played.
Actual: The music from the level played in Step 1 plays.

One level that could be used to reproduce this is Outrageous 14 from LPV, since LPV has no specified music rotation (every level has its music specified individually) and Outrageous 14 is specified to have no music.

[namida]

Duh, should've noticed my comments in step 1 and 2 were mutually exclusive (the level can't use the normal rotation, because this bug only occurs when the normal rotation is blank).

At any rate, fixed in commit b7c20b3.