Keep cash reserve policy backward compatible

Author: Pigbibi

main.py

@@ -234,7 +234,7 @@ def _env_flag(name: str) -> bool:
 NOTIFY_LANG = RUNTIME_SETTINGS.notify_lang
 
 CASH_RESERVE_RATIO = STRATEGY_RUNTIME.cash_reserve_ratio
-CASH_RESERVE_FLOOR_USD = STRATEGY_RUNTIME.cash_reserve_floor_usd
+CASH_RESERVE_FLOOR_USD = getattr(STRATEGY_RUNTIME, "cash_reserve_floor_usd", 0.0)
 REBALANCE_THRESHOLD_RATIO = 0.02
 LIMIT_BUY_PREMIUM = 1.005
 SELL_SETTLE_DELAY_SEC = 3