avformat/matroskadec: check generic audio deinterleaver sub_packet_size against frame_size

Fixes use of uninitialized memory
Fixes: msan_uninit-mem_7f67d052a530_7517_nosound.mkv
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
