xdg-shell: assert that configure events carry positive or zero sizes

Negative values here would indicate a compositor bug. For xdg_popup,
zero values are not allowed.

types/xdg_shell/wlr_xdg_popup.c

@@ -28,6 +28,7 @@ struct wlr_xdg_popup_configure *send_xdg_popup_configure(
 	}
 
 	struct wlr_box *geometry = &configure->geometry;
+	assert(geometry->width > 0 && geometry->height > 0);
 	xdg_popup_send_configure(popup->resource,
 		geometry->x, geometry->y,
 		geometry->width, geometry->height);

types/xdg_shell/wlr_xdg_toplevel.c

@@ -556,6 +556,7 @@ void wlr_xdg_toplevel_send_close(struct wlr_xdg_toplevel *toplevel) {
 
 uint32_t wlr_xdg_toplevel_set_size(struct wlr_xdg_toplevel *toplevel,
 		int32_t width, int32_t height) {
+	assert(width >= 0 && height >= 0);
 	toplevel->scheduled.width = width;
 	toplevel->scheduled.height = height;
 	return wlr_xdg_surface_schedule_configure(toplevel->base);