vaapisink: error handling if rendering fails
vaapisink: error handling if rendering fails

This patch enhance the code path when an error is found when rendering a
buffer.

If the video meta doesn't contain a surface proxy or a surface, a warning
message is printed.

If the rendering backend fails, a error message is posted in the bus.

https://bugzilla.gnome.org/show_bug.cgi?id=749382

01org/iotg-lin-gfx-gstreamer-vaapi,ceyusa/gstreamer-vaapi,01org/iotg-lin-gfx-gstreamer-vaapi,ceyusa/gstreamer-vaapi,CapOM/gstreamer-vaapi,CapOM/gstreamer-vaapi,GStreamer/gstreamer-vaapi,CapOM/gstreamer-vaapi,GStreamer/gstreamer-vaapi,01org/iotg-lin-gfx-gstreamer-vaapi