/locks should always respond, even if there's no locks

closes #4942

freqtrade/rpc/telegram.py

@@ -751,6 +751,9 @@ class Telegram(RPCHandler):
         Returns the currently active locks
         """
         rpc_locks = self._rpc._rpc_locks()
+        if not rpc_locks['locks']:
+            self._send_msg('No active locks.', parse_mode=ParseMode.HTML)
+
         for locks in chunks(rpc_locks['locks'], 25):
             message = tabulate([[
                 lock['id'],

tests/rpc/test_rpc_telegram.py

@@ -969,6 +969,11 @@ def test_telegram_lock_handle(default_conf, update, ticker, fee, mocker) -> None
     )
     telegram, freqtradebot, msg_mock = get_telegram_testobject(mocker, default_conf)
     patch_get_signal(freqtradebot, (True, False))
+    telegram._locks(update=update, context=MagicMock())
+    assert msg_mock.call_count == 1
+    assert 'No active locks.' in msg_mock.call_args_list[0][0][0]
+
+    msg_mock.reset_mock()
 
     PairLocks.lock_pair('ETH/BTC', arrow.utcnow().shift(minutes=4).datetime, 'randreason')
     PairLocks.lock_pair('XRP/BTC', arrow.utcnow().shift(minutes=20).datetime, 'deadbeef')