avfilter/vf_tmidequalizer: check that frame is valid

libavfilter/vf_tmidequalizer.c

@@ -178,6 +178,8 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *in)
         } else {
             s->l_frames++;
         }
+        if (!s->frames[idx])
+            return AVERROR_EOF;
         in = av_frame_clone(s->frames[idx]);
         if (!in)
             return AVERROR(ENOMEM);