Fix attempt for a traceback caused by removeTab... imglist Remove() on wxmac

gui/multiSwitch.py

@@ -88,7 +88,8 @@ class MultiSwitch(wx.Notebook):
             self.setTabTitle(i, None)
             remIcon = self.GetPageImage(i)
             self.SetPageImage(i, -1)
-            self.ImageList.Remove(remIcon)
+            if remIcon != -1:
+                self.ImageList.Remove(remIcon)
             page = self.GetPage(i)
             if page.type == "fit":
                 page.view.changeFit(None)