This allows testing EC and non EC. Avoids spending most time in EC on
high res samples and reduces the likelyhood of hitting timeouts

Fixes: Timeout in 467/fuzz-2-ffmpeg_VIDEO_AV_CODEC_ID_H263_fuzzer

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