wxGUI/gcpmanager: fix #430 (#447)

gui/wxpython/gcp/manager.py

@@ -1747,6 +1747,7 @@ class GCP(MapFrame, ColumnSorterMixin):
             self.TgtMap.Clean()
 
             self.grwiz.Cleanup()
+            self._mgr.UnInit()
 
             self.Destroy()