avcodec/mjpegdec: Check for odd progressive RGB

Fixes: out of array access
Fixes: 9225/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_JPEGLS_fuzzer-5684770334834688

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


Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit ee1e3ca5)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>