videoaggregator: Always set the pad's buffer_vinfo when storing a buffer

Otherwise it might be unset, and then the buffer is used and
gst_video_frame_map() will crash because of invalid video-info.

https://bugzilla.gnome.org/show_bug.cgi?id=753805

gst-libs/gst/video/gstvideoaggregator.c

@@ -1025,6 +1025,7 @@ gst_videoaggregator_fill_queues (GstVideoAggregator * vagg,
           GST_DEBUG_OBJECT (pad, "buffer duration is -1, start_time < "
               "output_start_time.  Discarding old buffer");
           gst_buffer_replace (&pad->buffer, buf);
+          pad->buffer_vinfo = *vinfo;
           gst_buffer_unref (buf);
           gst_aggregator_pad_drop_buffer (bpad);
           need_more_data = TRUE;