Fix unknown cursor in layer-shell example

examples/layer-shell.c

@@ -596,10 +596,16 @@ int main(int argc, char **argv) {
 	assert(cursor_theme);
 	struct wl_cursor *cursor =
 		wl_cursor_theme_get_cursor(cursor_theme, "crosshair");
+	if (cursor == NULL) {
+		cursor = wl_cursor_theme_get_cursor(cursor_theme, "left_ptr");
+	}
 	assert(cursor);
 	cursor_image = cursor->images[0];
 
 	cursor = wl_cursor_theme_get_cursor(cursor_theme, "tcross");
+	if (cursor == NULL) {
+		cursor = wl_cursor_theme_get_cursor(cursor_theme, "left_ptr");
+	}
 	assert(cursor);
 	popup_cursor_image = cursor->images[0];