Fixes: Infinite loop
Fixes: 34751/clusterfuzz-testcase-minimized-ffmpeg_dem_RPL_fuzzer-5439330800762880
Fixes: 34774/clusterfuzz-testcase-minimized-ffmpeg_dem_RPL_fuzzer-5851571660390400

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpegSigned-off-by: Michael Niedermayer <michael@niedermayer.cc>