Be careful removing windows from the list

I've occasionally had Python throw saying the window
isn't in the list.

gui/qt/__init__.py

@@ -163,13 +163,16 @@ class ElectrumGui:
         return w
 
     def close_window(self, window):
-        self.windows.remove(window)
+        # It seems that in some cases this can be called before the
+        # window is added to the windows list...
+        if window in self.windows:
+            self.windows.remove(window)
+            run_hook('on_close_window', window)
         self.build_tray_menu()
         # save wallet path of last open window
         if self.config.get('wallet_path') is None and not self.windows:
             path = window.wallet.storage.path
             self.config.set_key('gui_last_wallet', path)
-        run_hook('on_close_window', window)
 
     def main(self):
         self.timer.start()