avcodec/ffv1dec: Check for 0 quant tables

Fixes assertion failure
Fixes: 07ec1fc3c1cbf2d3edcd7d9b52ca156c/asan_heap-oob_13624c5_491_ecd4720a03e697ba750b235690656c8f.avi

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
