lavfi/audio: use av_samples_copy() instead of custom code.

Fixes a possible invalid write, found by Nicolas George.

libavfilter/audio.c

@@ -185,10 +185,6 @@ void ff_filter_samples(AVFilterLink *link, AVFilterBufferRef *samplesref)
     /* prepare to copy the samples if the buffer has insufficient permissions */
     if ((dst->min_perms & samplesref->perms) != dst->min_perms ||
         dst->rej_perms & samplesref->perms) {
-        int  i, planar = av_sample_fmt_is_planar(samplesref->format);
-        int planes = !planar ? 1:
-                     av_get_channel_layout_nb_channels(samplesref->audio->channel_layout);
-
         av_log(link->dst, AV_LOG_DEBUG,
                "Copying audio data in avfilter (have perms %x, need %x, reject %x)\n",
                samplesref->perms, link->dstpad->min_perms, link->dstpad->rej_perms);
@@ -199,8 +195,10 @@ void ff_filter_samples(AVFilterLink *link, AVFilterBufferRef *samplesref)
         link->cur_buf->audio->sample_rate = samplesref->audio->sample_rate;
 
         /* Copy actual data into new samples buffer */
-        for (i = 0; i < planes; i++)
-            memcpy(link->cur_buf->extended_data[i], samplesref->extended_data[i], samplesref->linesize[0]);
+        av_samples_copy(link->cur_buf->extended_data, samplesref->extended_data,
+                        0, 0, samplesref->audio->nb_samples,
+                        av_get_channel_layout_nb_channels(link->channel_layout),
+                        link->format);
 
         avfilter_unref_buffer(samplesref);
     } else