Browser Development • DoesTextureSharingWorkInternal crashes on wine because no keyed mutex support.

Wine doesn't support IDXGIKeyedMutex currently. So the function DoesTextureSharingWorkInternal in XUL's gfx/thebes/D3D11Checks.cpp crashes in wine because it doesn't check whether the QueryInterface for the IDXGIKeyedMutex succeeds or not, but it should. In other parts of the code base, it's almost always checked (unless implied prior to be available), I think here it should be checked too for FAILED or NULL sourceSharedMutex.

Without this it works fine btw.

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