wsi/x11: Fix a misunderstanding about how xcb_get_geometry works
The code here is well-intentioned, but the only way a GetGeometry request can fail is if you name an invalid drawable. And if we did that, either our internal state got corrupted, or - more likely - the user destroyed the window. In either case there's nothing more we can do with the surface, so report that it's been lost.
@jekstrand original error case code here was yours, did I miss something subtle here?