This crash occurred when an audio stream finished playing in NOTIFICATION_INTERNAL_PROCESS,
during which it would iterate through a loop of playbacks,
leading to a "finished" signal, which removed the audio player from the tree
which led to a NOTIFICATION_EXIT_TREE,
which would mutate the array of playbacks while within the above loop.
This moves the signal callback outside of the loop which avoids the crash.
Note: previously, the signal was called multiple times if the same player finishes multiple times in one frame. Now it is at most once per frame.
Affects AudioStreamPlayer, AudioStreamPlayer2D and AudioStreamPlayer3D
c088a2dd89