BT: Update trade open_rate on first filled order.

freqtrade/optimize/backtesting.py

@@ -813,6 +813,11 @@ class Backtesting:
                 cost=stake_amount + trade.fee_open,
             )
             if pos_adjust and self._get_order_filled(order.price, row):
+                # Update trade open_rate on first filled order
+                # this is for cases where adjust_entry_order might have replaced the
+                # initial order from trade opening
+                if len(trade.select_filled_orders(trade.entry_side)) == 1:
+                    trade.open_rate = order.price
                 order.close_bt_order(current_time)
             else:
                 trade.open_order_id = str(self.order_id_counter)