avfilter/framesync: fix OOM case

Fixes OOM when caller keeps adding frames into filtergraph
that reached EOF by other means, for example EOF is signalled
by other filter in filtergraph or by buffersink.

libavfilter/framesync.c

@@ -354,8 +354,11 @@ static int consume_from_fifos(FFFrameSync *fs)
 
 int ff_framesync_activate(FFFrameSync *fs)
 {
+    AVFilterContext *ctx = fs->parent;
     int ret;
 
+    FF_FILTER_FORWARD_STATUS_BACK_ALL(ctx->outputs[0], ctx);
+
     ret = framesync_advance(fs);
     if (ret < 0)
         return ret;