Check xdg_surface's role before using its toplevel

Don't access xdg_surface->toplevel if xdg_surface->role is equal to
WLR_XDG_SURFACE_ROLE_NONE, since this could lead to crash. The same
checks are added for xdg_surface_v6.

Fixes #3311

sway/desktop/xdg_shell.c

@@ -216,7 +216,7 @@ static bool is_transient_for(struct sway_view *child,
 		return false;
 	}
 	struct wlr_xdg_surface *surface = child->wlr_xdg_surface;
-	while (surface) {
+	while (surface && surface->role == WLR_XDG_SURFACE_ROLE_TOPLEVEL) {
 		if (surface->toplevel->parent == ancestor->wlr_xdg_surface) {
 			return true;
 		}

sway/desktop/xdg_shell_v6.c

@@ -213,7 +213,7 @@ static bool is_transient_for(struct sway_view *child,
 		return false;
 	}
 	struct wlr_xdg_surface_v6 *surface = child->wlr_xdg_surface_v6;
-	while (surface) {
+	while (surface && surface->role == WLR_XDG_SURFACE_V6_ROLE_TOPLEVEL) {
 		if (surface->toplevel->parent == ancestor->wlr_xdg_surface_v6) {
 			return true;
 		}

sway/tree/container.c

@@ -341,7 +341,7 @@ static bool surface_is_popup(struct wlr_surface *surface) {
 	if (wlr_surface_is_xdg_surface(surface)) {
 		struct wlr_xdg_surface *xdg_surface =
 			wlr_xdg_surface_from_wlr_surface(surface);
-		while (xdg_surface) {
+		while (xdg_surface && xdg_surface->role != WLR_XDG_SURFACE_ROLE_NONE) {
 			if (xdg_surface->role == WLR_XDG_SURFACE_ROLE_POPUP) {
 				return true;
 			}
@@ -353,7 +353,8 @@ static bool surface_is_popup(struct wlr_surface *surface) {
 	if (wlr_surface_is_xdg_surface_v6(surface)) {
 		struct wlr_xdg_surface_v6 *xdg_surface_v6 =
 			wlr_xdg_surface_v6_from_wlr_surface(surface);
-		while (xdg_surface_v6) {
+		while (xdg_surface_v6 &&
+				xdg_surface_v6->role != WLR_XDG_SURFACE_V6_ROLE_NONE) {
 			if (xdg_surface_v6->role == WLR_XDG_SURFACE_V6_ROLE_POPUP) {
 				return true;
 			}