wxGUI/g.gui.image2target: fix close window (dissociate the managed window from the AuiManager) (#1038)

gui/wxpython/image2target/ii2t_manager.py

@@ -1814,6 +1814,7 @@ class GCP(MapFrame, ColumnSorterMixin):
             self.TgtMap.Clean()
 
             self.grwiz.Cleanup()
+            self._mgr.UnInit()
 
             self.Destroy()