When using SteamVR without starting SteamVR, the physical device cannot
be found. This isn't reported to the user nicely. This change will
tell the user why OpenXR couldn't be started.
Note that the physical device can be created when SteamVR has already
launched. OpenGL will start SteamVR automatically, but seems Vulkan
isn't able to do that.
566c3d0846