UpdateSounds will not be called during screen wipes and the entire setup of this function suggests that this is not advisable at all.
The OpenAL stream updates were done deep inside this function implicitly.
This caused music to stop while a wipe was in progress. So in order to allow uninterrupted music playback during screen wipes the music updates need to be handled separately from sound updates and be called both in the main loop and the wipe loop.
I think that the OpenAL music updating should be offloaded to a separate thread but at least it's working now without causing interruptions during wipes.
Instead of the previous method where there'd be a filename and offset, and/or a
memory pointer, this uses a class to access resource data regardless of its
underlying form.
