avcodec/interplayvideo: Check that enough data is available for opcode_0x9

Fixes use of uninitialized memory
Fixes: msan_uninit-mem_7fd5185b45df_5895_interplay-logo-2MB.mve
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
