This is not a fix, but it temporarily works around the potential crash
discussed here https://github.com/open-goal/jak-project/issues/2988
As long as this doesn't impact other things, this feels like a good
interim fix, as having a broken cutscene is better than a fatal crash
and it might be some time before this is properly identified and fixed.
Normally, when they allocate a VagCmd, they do a bunch of stuff to clear
all the status bits and reset things
in particular the InitVAGCmd function does a lot

but for the stereo command, they do a lot less:

Which means that the new_stereo_command can just have random status bits
left over from whatever the last user had.
we seem to end up in a state where byte21 is set, and this causes
everything else to be wrong and off-by-one dma transfer. My guess is
that the original game avoided this bug due to lucky timing that I don't
understand.
I think the fix of just clearing byte21 is ok because there's no way
that the old value of the byte is useful after the command is
repurposed.