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
8 jobs from deint in 16 minutes and 33 seconds (queued for 3 seconds)
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gst indent

00:00:19

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manifest

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build fedora x86_64

00:03:40

 
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check fedora

00:03:38

 
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build android arm64 api28

00:05:23

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build cerbero cross win32

00:07:28

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build cerbero cross win64

00:08:41

passed #79569
build cerbero fedora x86_64

00:07:59