primitivus: don't focus on new widget if one is already selected:

new widgets were getting focus even when one was already selected.

fix 326

sat_frontends/primitivus/primitivus

@@ -643,7 +643,8 @@ class PrimitivusApp(QuickApp, InputHistory):
     def newWidget(self, widget):
         # FIXME: when several widgets are possible (e.g. with :split)
         #        do not replace current widget when self.selected_widget != None
-        self.selectWidget(widget)
+        if self.selected_widget is None:
+            self.selectWidget(widget)
 
     def selectWidget(self, widget):
         """Display a widget if possible,