asyncts: reset delta to 0 when it's not used.

Fixes an invalid write.

libavfilter/af_asyncts.c

@@ -182,11 +182,14 @@ static void filter_samples(AVFilterLink *inlink, AVFilterBufferRef *buf)
     if (labs(delta) > s->min_delta) {
         av_log(ctx, AV_LOG_VERBOSE, "Discontinuity - %"PRId64" samples.\n", delta);
         out_size += delta;
-    } else if (s->resample) {
+    } else {
+        if (s->resample) {
             int comp = av_clip(delta, -s->max_comp, s->max_comp);
             av_log(ctx, AV_LOG_VERBOSE, "Compensating %d samples per second.\n", comp);
             avresample_set_compensation(s->avr, delta, inlink->sample_rate);
         }
+        delta = 0;
+    }
 
     if (out_size > 0) {
         AVFilterBufferRef *buf_out = ff_get_audio_buffer(outlink, AV_PERM_WRITE,