Core: Assign an explicit parent for main editor area

This avoids failing updates of the main window (e.g. windowTitle)
before the main editor area is displayed first time.

Change-Id: I5c559f9487872e47b1fd914f0aec16b0b2f1dec3
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/coreplugin/editormanager/editormanager.cpp

@@ -442,6 +442,8 @@ void EditorManagerPrivate::init()
 
     // other setup
     auto mainEditorArea = new EditorArea();
+    // assign parent to avoid failing updates (e.g. windowTitle) before it is displayed first time
+    mainEditorArea->setParent(ICore::mainWindow());
     mainEditorArea->hide();
     connect(mainEditorArea, &EditorArea::windowTitleNeedsUpdate,
             this, &EditorManagerPrivate::updateWindowTitle);