PartDesign: closing task dialog when exiting edit mode for Primitives

=====================================================================

fixes #4241

Problem:

PartDesignGui::ViewProvider is responsible for closing the tasks for most of PD features when exiting edit mode
(i.e. unsetEdit()).

For primitives, PartDesignGui::ViewProviderPrimitive is responsible, and neither does it or relies on its parent
VP to do it when calling unsetEdit().

Solution:

Make PartDesignGui::ViewProviderPrimitive::unsetEdit() rely on parent PartDesignGui::ViewProvider to tidy up,
including closing the task dialog.

Reference:

This is the default stack call when closing a document while a PD task using PartDesignGui::Viewprovider is active:

src/Mod/PartDesign/Gui/ViewProviderPrimitive.cpp

@@ -123,8 +123,12 @@ bool ViewProviderPrimitive::setEdit(int ModNum)
 
 void ViewProviderPrimitive::unsetEdit(int ModNum)
 {
-    Q_UNUSED(ModNum);
     setPreviewDisplayMode(false);
+
+    // Rely on parent class to:
+    // restitute old workbench (set setEdit above) and close the dialog if exiting editing
+    PartDesignGui::ViewProvider::unsetEdit(ModNum);
+
 }
 
 void ViewProviderPrimitive::updateData(const App::Property* p) {