fix plugin load_wallet hook

plugins/btchipwallet.py

@@ -74,6 +74,8 @@ class Plugin(BasePlugin):
 
     @hook
     def load_wallet(self, wallet, window):
+        self.wallet = wallet
+        self.window = window
         if self.btchip_is_connected():
             if not self.wallet.check_proper_device():
                 QMessageBox.information(self.window, _('Error'), _("This wallet does not match your BTChip device"), _('OK'))