Song playing issue in Chunky Phase final cutscene

[theballaam96]

https://www.twitch.tv/jxjacob/clip/MushyGleamingClipsmomSeemsGood-_5nXc4NNse8Ma4wy

[AlmostSeagull]

Probably want to make a function to end whatever the boss song is, rather than relying on vanilla code with its assumption that people wouldn't change the game to play different songs there.

[AlmostSeagull]

Going to add minibosses to this issue, so not moving it to Needs Testing yet, but all main boss music should now behave correctly.