Backport of "d3d11videosink/win32 window: fix race condition in unprepare" into 1.22
requested to merge tpm/gstreamer:backport-mr-4260-into-1.22-d3d11videosink-fix-unprepare-race-condition into 1.22
Backport of !4260 (merged) "d3d11videosink/win32 window: fix race condition in unprepare".
Commits: