A few fixes for the Wayland backend.

• The error handling is kinda important; without it, the compositor can decide to close the window with Miniquad busy looping in the background and consuming 100% CPU usage, which would be very bad for a clueless end user.
• Handle dpi scale change in runtime. This is where I ran into the error handling issue: if you have a window with size say 801x600, changing dpi to 2x would end up with a protocol error saying that 801 is not a multiple of 2. There's still some issue with the current implementation, as after a dpi scale change the first few frames would not be rendered correctly. But at least it's not crashing, and I think changing dpi really doesn't happen that frequently so no more Wayland's "every frame is perfect" 🤷