wl_egl: close fence_fd when gsource finalized

wl_egl: close fence_fd when gsource finalized

 - Even though when main thread have called tpl_gsource_destroy for
  fence_waiting_source, which has not yet signaled, gsource may not be
  completely destroyed because it might be in dispatch queue in g_main_context.

 - In this case, if the fence_waiting_source is dispatched, it can try
  to commit with the invalid wl_egl_buffer that has already been freed.

 - This commit makes to prevent operating with an invalid wl_egl_buffer
  and to close fence_fd properly.

Change-Id: I6ff30925f1bed6806017d408bf1bf067eab6624b
Signed-off-by: Joonbum Ko <joonbum.ko@samsung.com>