OSV-2020-1242 Heap-buffer-overflow in ih264d_cavlc_parse4x4coeff_n8

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=16587 Crash type: Heap-buffer-overflow READ 4 Crash state: ih264dcavlcparse4x4coeffn8 ih264dcavlcparse8x8blockbothavailable ih264dparseresidual4x4cavlc...