wlr_renderer_destroy: fix renderer NULL check

renderer is checked for NULL, but was dereferenced before that.

Found through static analysis

render/wlr_renderer.c

@@ -25,9 +25,12 @@ void wlr_renderer_init(struct wlr_renderer *renderer,
 }
 
 void wlr_renderer_destroy(struct wlr_renderer *r) {
+	if (!r) {
+		return;
+	}
 	wlr_signal_emit_safe(&r->events.destroy, r);
 
-	if (r && r->impl && r->impl->destroy) {
+	if (r->impl && r->impl->destroy) {
 		r->impl->destroy(r);
 	} else {
 		free(r);