avcodec/indeo4: Check remaining data in Pic hdr extension parsing code

Fixes: Timeout
Fixes: 2115/clusterfuzz-testcase-minimized-6594111748440064

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