Fix #7303, Quad node mesh data leak

(cherry picked from commit 7504a015aa5637449aa2c69a3c11b521ff71225d)

scene/3d/quad.cpp

@@ -230,3 +230,7 @@ Quad::Quad() {
 	configured=false;
 
 }
+
+Quad::~Quad() {
+	VisualServer::get_singleton()->free(mesh);
+}

scene/3d/quad.h

@@ -71,6 +71,7 @@ public:
 	virtual AABB get_aabb() const;
 
 	Quad();
+	~Quad();
 };