desktop-shell: Handle the fullscreen to maximized case safely

When a client transitions from maximized to fullscreen to maximized (run
weston-terminal, maximize it, hit f11 twice) we're sending size 0,0 for
the unfullscreen configure, which still has maximized set.

This results in clients correctly picking any size they like, and weston
disconnecting them for it.

Instead, pass the correct maximized size.

Signed-off-by: Derek Foreman <derekf@osg.samsung.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>

desktop-shell/shell.c

@@ -2618,6 +2618,8 @@ set_fullscreen(struct shell_surface *shsurf, bool fullscreen,
 
 		width = shsurf->output->width;
 		height = shsurf->output->height;
+	} else if (weston_desktop_surface_get_maximized(desktop_surface)) {
+		get_maximized_size(shsurf, &width, &height);
 	}
 	weston_desktop_surface_set_fullscreen(desktop_surface, fullscreen);
 	weston_desktop_surface_set_size(desktop_surface, width, height);