QmlDesigner: Avoid second error message

We get editingFinished twice. By checking visible we able to ignore
the second signal.

Change-Id: Ic5ab91e153b1d658a68321436c71b914e065c6dd
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

share/qtcreator/qmldesigner/propertyEditorQmlSources/QtQuick/ItemPane.qml

@@ -90,8 +90,9 @@ Rectangle {
                                 fixedSize: true
 
                                 onEditingFinished: {
+                                    if (visible)
+                                        changeTypeName(typeLineEdit.text.trim())
                                     visible = false
-                                    changeTypeName(typeLineEdit.text.trim())
                                 }
                             }