avcodec/dfa: Fix: runtime error: signed integer overflow: -14202 * 196877 cannot be represented in type 'int'

Fixes: 1657/clusterfuzz-testcase-minimized-4710000079405056

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