IVRTrackedCamera::GetVideoStreamFrameBuffer crash/hang with Vulkan

[Rectus]

Attempting to retrieve the passthrough camera framebuffer with IVRTrackedCamera::GetVideoStreamFrameBuffer() while the scene application is rendering with Vulkan causes the application either to crash with an invalid memory access inside the function, or it to hang on any rendering calls that wait for fences. This happens consistently a few seconds after launching the application.

This affects scene applications using both OpenVR and OpenXR. I have tested it with both my application and Unreal 4.27 with consistent results, so it is unlikely it is cause by application-side Vulkan code.

Tested on SteamVR beta 1.25.3 and Windows 10 with a Valve Index.