x11: Catch X11 errors in X11_SetWindowPosition and X11_SetWindowSize. The functions can go south if other operations are in progress, like X11_SetWindowBordered, which might be doing something traumatic behind the scenes of the window manager. We can't make these tasks totally synchronous, which would fix the problem, because not only can the window manager block however long it wants, it might also decide to deny our requests without any notification, so we'd be waiting forever for a window change that isn't coming. :( Fixes #5274.