IMplement check for unlimited settings

verifying that either max_open_trades or stake_amount is set for
operations without edge

freqtrade/configuration/config_validation.py

@@ -67,12 +67,24 @@ def validate_config_consistency(conf: Dict[str, Any]) -> None:
     _validate_trailing_stoploss(conf)
     _validate_edge(conf)
     _validate_whitelist(conf)
+    _validate_unlimited_amount(conf)
 
     # validate configuration before returning
     logger.info('Validating configuration ...')
     validate_config_schema(conf)
 
 
+def _validate_unlimited_amount(conf: Dict[str, Any]) -> None:
+    """
+    If edge is disabled, either max_open_trades or stake_amount need to be set.
+    :raise: OperationalException if config validation failed
+    """
+    if (not conf.get('edge', {}).get('enabled')
+       and conf.get('max_open_trades') == float('inf')
+       and conf.get('stake_amount') == constants.UNLIMITED_STAKE_AMOUNT):
+        raise OperationalException("`max_open_trades` and `stake_amount` cannot both be unlimited.")
+
+
 def _validate_trailing_stoploss(conf: Dict[str, Any]) -> None:
 
     if conf.get('stoploss') == 0.0:

tests/test_configuration.py

@@ -722,6 +722,14 @@ def test_validate_default_conf(default_conf) -> None:
     validate_config_schema(default_conf)
 
 
+def test_validate_max_open_trades(default_conf):
+    default_conf['max_open_trades'] = float('inf')
+    default_conf['stake_amount'] = 'unlimited'
+    with pytest.raises(OperationalException, match='`max_open_trades` and `stake_amount` '
+                                                   'cannot both be unlimited.'):
+        validate_config_consistency(default_conf)
+
+
 def test_validate_tsl(default_conf):
     default_conf['stoploss'] = 0.0
     with pytest.raises(OperationalException, match='The config stoploss needs to be different '