avcodec/qtrle: Check remaining bytestream in qtrle_decode_XYbpp()

Fixes: Timeout
Fixes: 9213/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_QTRLE_fuzzer-5649753332252672

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg


Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>