v4l2bufferpool: Workaround elements not requesting any buffers

This is a workaround for element that don't request buffers when
they should.

https://bugzilla.gnome.org/show_bug.cgi?id=732288

sys/v4l2/gstv4l2bufferpool.c

@@ -718,6 +718,12 @@ gst_v4l2_buffer_pool_start (GstBufferPool * bpool)
   else
     max_latency = min_buffers;
 
+  /* FIXME Encoder don't negotiate amount of buffers. If we can't grow the
+   * pool, or the minimum is at V4L2 maximum, enabled copy on threshold
+   * https://bugzilla.gnome.org/show_bug.cgi?id=732288 */
+  if (!can_allocate || min_buffers == VIDEO_MAX_FRAME)
+    copy_threshold = min_latency;
+
   pool->size = size;
   pool->copy_threshold = copy_threshold;
   pool->max_latency = max_latency;