#3209 Make sure project tree is initialised when creating the plot window.

* Also ensure the main plot window is created before attempting to set a brand new plot as an MDI window.
* This ensures the MDI view controller has been created, otherwise the new plot MDI window will not be shown in the main plot window when the main plot window is created.

ApplicationCode/Application/RiaApplication.cpp

@@ -1355,6 +1355,8 @@ RiuPlotMainWindow* RiaApplication::getOrCreateMainPlotWindow()
     if (!m_mainPlotWindow)
     {
         createMainPlotWindow();
+        m_mainPlotWindow->initializeGuiNewProjectLoaded();
+        loadAndUpdatePlotData();
     }
     return m_mainPlotWindow;
 }