libs: window: wayland: rt event queue at destroy()
libs: window: wayland: rt event queue at destroy()

The proxy object of wl_buffer for the last frame remains in the
wl_map. Even though we call wl_buffer_destory() in
frame_release_callback(), the proxy object remains without being
removed, since proxy object is deleted when wayland server sees the
delete request and send 'delete_id' event.

We need to call roundtrip before destroying event_queue so that the
proxy object is removed. Otherwise, it would be mess up as receiving
'delte_id' event from previous play, when playing in the next
va/wayland_window with the same wl_display connection.

This code fixed is porting from gst-vaapi commit id:
896a836f1dcd52c08d6ebcd5045d47036dce5854

Fixes #44

Signed-off-by: Lim Siew Hoon <e412356d7e67dbdde94e841e5d46937fb9f4e623@intel.com>

ph0b/gstreamer-media-SDK,ishmael1985/gstreamer-media-SDK