wayland: Be more careful when destroying windows
wayland: Be more careful when destroying windows

We call gdk_wayland_window_hide_surface when the window gets
destroyed, and in this case, the frame clock might not exist
anymore.

This was showing up in the displayclose testcase.

jadahl/gtk,chergert/gtk,davidgumberg/gtk,chergert/gtk,jigpu/gtk,chergert/gtk,jadahl/gtk,chergert/gtk,grubersjoe/adwaita,chergert/gtk,alexlarsson/gtk,alexlarsson/gtk,alexlarsson/gtk,alexlarsson/gtk,jigpu/gtk,chergert/gtk,jadahl/gtk,grubersjoe/adwaita,jadahl/gtk,alexlarsson/gtk,jigpu/gtk,chergert/gtk,jadahl/gtk,davidgumberg/gtk,jadahl/gtk,chergert/gtk,davidgumberg/gtk,alexlarsson/gtk,grubersjoe/adwaita,jadahl/gtk,grubersjoe/adwaita,jigpu/gtk,davidgumberg/gtk,davidgumberg/gtk,davidgumberg/gtk,jigpu/gtk,grubersjoe/adwaita,grubersjoe/adwaita,jigpu/gtk,alexlarsson/gtk,alexlarsson/gtk,davidgumberg/gtk,grubersjoe/adwaita,davidgumberg/gtk,grubersjoe/adwaita,jigpu/gtk,jigpu/gtk,jadahl/gtk