view: Handle NULL role object when role is set

wlr_(xdg|xwayland)_surface_from_wlr_surface can return NULL even though
wlr_surface_is_(xdg|xwayland)_surface returned true.

sway/tree/view.c

@@ -1139,12 +1139,18 @@ struct sway_view *view_from_wlr_surface(struct wlr_surface *wlr_surface) {
 	if (wlr_surface_is_xdg_surface(wlr_surface)) {
 		struct wlr_xdg_surface *xdg_surface =
 			wlr_xdg_surface_from_wlr_surface(wlr_surface);
+		if (xdg_surface == NULL) {
+			return NULL;
+		}
 		return view_from_wlr_xdg_surface(xdg_surface);
 	}
 #if HAVE_XWAYLAND
 	if (wlr_surface_is_xwayland_surface(wlr_surface)) {
 		struct wlr_xwayland_surface *xsurface =
 			wlr_xwayland_surface_from_wlr_surface(wlr_surface);
+		if (xsurface == NULL) {
+			return NULL;
+		}
 		return view_from_wlr_xwayland_surface(xsurface);
 	}
 #endif