rtpbasepayload: don't write empty extension header

When some header extensions are present but none decides to write any
data to the currently processed RTP buffer, remove the extension data
section.

Resulting RTP buffer wasn't formatted correctly.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/-/merge_requests/1173>

gst-libs/gst/rtp/gstrtpbasepayload.c

@@ -1764,13 +1764,17 @@ set_headers (GstBuffer ** buffer, guint idx, gpointer user_data)
     g_ptr_array_foreach (data->payload->priv->header_exts,
         (GFunc) write_header_extension, &hdrext);
 
-    wordlen = hdrext.written_size / 4 + ((hdrext.written_size % 4) ? 1 : 0);
+    if (hdrext.written_size > 0) {
+      wordlen = hdrext.written_size / 4 + ((hdrext.written_size % 4) ? 1 : 0);
 
-    /* zero-fill the hdrext padding bytes */
-    memset (&hdrext.data[hdrext.written_size], 0,
-        wordlen * 4 - hdrext.written_size);
+      /* zero-fill the hdrext padding bytes */
+      memset (&hdrext.data[hdrext.written_size], 0,
+          wordlen * 4 - hdrext.written_size);
 
-    gst_rtp_buffer_set_extension_data (&rtp, bit_pattern, wordlen);
+      gst_rtp_buffer_set_extension_data (&rtp, bit_pattern, wordlen);
+    } else {
+      gst_rtp_buffer_remove_extension_data (&rtp);
+    }
   }
   GST_OBJECT_UNLOCK (data->payload);
   gst_rtp_buffer_unmap (&rtp);