Add check to ensure close_profit_abs is filled on closed trades

Technically, this should not be possible, but #4554 shows it is.

closes #4554

freqtrade/wallets.py

@@ -71,7 +71,8 @@ class Wallets:
         # TODO: potentially remove the ._log workaround to determine backtest mode.
         if self._log:
             closed_trades = Trade.get_trades_proxy(is_open=False)
-            tot_profit = sum([trade.close_profit_abs for trade in closed_trades])
+            tot_profit = sum(
+                [trade.close_profit_abs for trade in closed_trades if trade.close_profit_abs])
         else:
             tot_profit = LocalTrade.total_profit
         tot_in_trades = sum([trade.stake_amount for trade in open_trades])