query_info: raise if user cancelled

gui/qt/main_window.py

@@ -1288,7 +1288,8 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, PrintError):
         vbox = QVBoxLayout(dialog)
         vbox.addLayout(clayout.layout())
         vbox.addLayout(Buttons(OkButton(dialog)))
-        dialog.exec_()
+        if not dialog.exec_():
+            return None
         return clayout.selected_index()
 
     def lock_amount(self, b):

lib/plugins.py

@@ -472,7 +472,10 @@ class DeviceMgr(ThreadJob, PrintError):
                 return info
         msg = _("Please select which %s device to use:") % plugin.device
         descriptions = [info.label + ' (%s)'%(_("initialized") if info.initialized else _("wiped")) for info in infos]
-        info = infos[handler.query_choice(msg, descriptions)]
+        c = handler.query_choice(msg, descriptions)
+        if c is None:
+            raise UserCancelled()
+        info = infos[c]
         # save new label
         keystore.set_label(info.label)
         keystore.handler.win.wallet.save_keystore()