QmlDesigner: call resetSelectionLocked() when attaching new model

This ensures that the property editor is not staying locked,
when switching files.

Change-Id: Iaa2b6333fb51b61eaeb78b973704d0f6546dec3e
Reviewed-by: Miikka Heikkinen <miikka.heikkinen@qt.io>

src/plugins/qmldesigner/components/propertyeditor/propertyeditorview.cpp

@@ -890,6 +890,7 @@ void PropertyEditorView::modelAttached(Model *model)
     if (debug)
         qDebug() << Q_FUNC_INFO;
 
+    resetSelectionLocked();
     resetView();
 }