This prevents Blender from crashing with an access violation when
stopping a VR session using the DirectX backend. The issue occurred for
any headset on Windows+Nvidia when using the SteamVR runtime and thus
affected a large number of users.
The workaround presented here is to simply skip unregistering the
shared resources on exit, as either of the calls to
`wglDXUnregisterObjectNV()` or `wglDXCloseDeviceNV()` will result in an
access violation. While not ideal, this avoids the crash and doesn't
present any issues when starting a new VR session.
Reviewed By: Severin
Differential Revision: https://developer.blender.org/D16569
db28a8b3d1