Check if timeframe is available before calling exchange

closes #6517

tests/exchange/test_exchange.py

@@ -1692,6 +1692,13 @@ def test_refresh_latest_ohlcv(mocker, default_conf, caplog) -> None:
                                         cache=False)
     assert len(res) == 3
     assert exchange._api_async.fetch_ohlcv.call_count == 3
+    exchange._api_async.fetch_ohlcv.reset_mock()
+    caplog.clear()
+    # Call with invalid timeframe
+    res = exchange.refresh_latest_ohlcv([('IOTA/ETH', '3m')],cache=False)
+    assert not res
+    assert len(res) == 0
+    assert log_has_re(r'Cannot download \(IOTA\/ETH, 3m\).*', caplog)
 
 
 @pytest.mark.asyncio