d3d11videosink: blocked when changing state READY to NULL

Test environment

• Windows 10 msvc
• run with external window handle from gtk DrawingArea

D3d11videosink gets blocked ShowWindow (self->internal_hwnd, SW_HIDE) while doing some destroying steps in READY to NULL state.

https://gitlab.freedesktop.org/gstreamer/gstreamer/-/blob/main/subprojects/gst-plugins-bad/sys/d3d11/gstd3d11window_win32.cpp#L211