QmlDesigner: Fix resolving of source

Using the QUrl:resolve() does not work with Qt 5.9.
Since the file url is a local file and not directory this was
weird usage of QUrl anyway.

Change-Id: I2d709bc40a404b61ea3c3edbbfd1727a6ee2111c
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/plugins/qmldesigner/documentmanager.cpp

@@ -148,9 +148,9 @@ static void openSourcePropertyOfLoader(const ModelNode &modelNode)
     QmlDesignerPlugin::instance()->viewManager().nextFileIsCalledInternally();
 
     QString componentFileName = modelNode.variantProperty("source").value().toString();
-    QString componentFilePath = modelNode.model()->fileUrl().resolved(QUrl::fromLocalFile(componentFileName)).toLocalFile();
 
-    Core::EditorManager::openEditor(componentFilePath, Core::Id(), Core::EditorManager::DoNotMakeVisible);
+    QFileInfo fileInfo(modelNode.model()->fileUrl().toLocalFile());
+    Core::EditorManager::openEditor(fileInfo.absolutePath() + "/" + componentFileName, Core::Id(), Core::EditorManager::DoNotMakeVisible);
 }