fftools/ffmpeg_filter: do not flush encoders on parameter change

It makes no sense to do so.

fftools/ffmpeg_filter.c

@@ -1905,7 +1905,7 @@ int ifilter_send_frame(InputFilter *ifilter, AVFrame *frame, int keep_reference)
             return ret;
         }
 
-        ret = reap_filters(1);
+        ret = reap_filters(0);
         if (ret < 0 && ret != AVERROR_EOF) {
             av_log(NULL, AV_LOG_ERROR, "Error while filtering: %s\n", av_err2str(ret));
             return ret;