avcodec/cfhd: Check band parameters before storing them

Fixes out of array read
Fixes: 2169/clusterfuzz-testcase-minimized-5688641642823680

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