Tweaked Make Selected into Reference.

Having dupes from ref folders (which makes ref switching impossible) would make
the new feature glitchy (selection would be emptied). Now, in cases where the action
results in nothing being changed, the selection stays intact. [#222]

core/results.py

@@ -244,8 +244,9 @@ class Results(Markable):
     def make_ref(self, dupe):
         g = self.get_group_of_duplicate(dupe)
         r = g.ref
+        if not g.switch_ref(dupe):
+            return False
         self._remove_mark_flag(dupe)
-        g.switch_ref(dupe);
         if not r.is_ref:
             self.__total_count += 1
             self.__total_size += r.size
@@ -254,6 +255,7 @@ class Results(Markable):
             self.__total_size -= dupe.size
         self.__dupes = None
         self.is_modified = True
+        return True
     
     def perform_on_marked(self, func, remove_from_results):
         # Performs `func` on all marked dupes. If an EnvironmentError is raised during the call,