avcodec/indeo2: Check remaining bits in ir2_decode_plane()

Fixes: 1290/clusterfuzz-testcase-minimized-5815578902134784
Fixes: timeout

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