Clear connection from/to empty after used

The connection data provided by _connection_from_empty and
_connection_to_empty was not cleared and caused unwanted
connections in some cases.

editor/plugins/visual_shader_editor_plugin.cpp

@@ -1808,6 +1808,7 @@ VisualShaderNode *VisualShaderEditor::_add_node(int p_idx, int p_op_idx) {
 			}
 		}
 	}
+	_member_cancel();
 
 	VisualShaderNodeUniform *uniform = Object::cast_to<VisualShaderNodeUniform>(vsnode.ptr());
 	if (uniform) {