Add a check to prevent duplicating connections in visual shader

scene/resources/visual_shader.cpp

@@ -967,6 +967,12 @@ void VisualShader::connect_nodes_forced(Type p_type, int p_from_node, int p_from
 	ERR_FAIL_COND(!g->nodes.has(p_to_node));
 	ERR_FAIL_INDEX(p_to_port, g->nodes[p_to_node].node->get_input_port_count());
 
+	for (const Connection &E : g->connections) {
+		if (E.from_node == p_from_node && E.from_port == p_from_port && E.to_node == p_to_node && E.to_port == p_to_port) {
+			return;
+		}
+	}
+
 	Connection c;
 	c.from_node = p_from_node;
 	c.from_port = p_from_port;