vaapipostproc: before set surface proxy, check if it already been created and exist.
vaapipostproc: before set surface proxy, check if it already been created and exist.

Fix the deinterlace black frame when playing with glimagesink:
gst-launch-1.0 filesrc location=test.264 ! h264parse ! vaapih264dec \
! vaapipostproc deinterlace-mode=1 deinterlace-method=1 ! glimagesink

GStreamer/gstreamer-vaapi,GStreamer/gstreamer-vaapi,ceyusa/gstreamer-vaapi,ceyusa/gstreamer-vaapi