avcodec/interplayvideo: Clean up frames on parameter change

Fixes: out of array access
Fixes: 2467/clusterfuzz-testcase-minimized-4755798049685504

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