fix: validation error on reconciling PE to Journals as Invoice

With the same exchange rate on Journal Entry and Payment Entry,
reconcilition should not post exc gain/loss journal and should not
throw validation error

(cherry picked from commit 5eeb650)

erpnext/accounts/utils.py

@@ -626,8 +626,10 @@ def update_reference_in_payment_entry(
 		"total_amount": d.grand_total,
 		"outstanding_amount": d.outstanding_amount,
 		"allocated_amount": d.allocated_amount,
-		"exchange_rate": d.exchange_rate if d.exchange_gain_loss else payment_entry.get_exchange_rate(),
-		"exchange_gain_loss": d.exchange_gain_loss,
+		"exchange_rate": d.exchange_rate
+		if d.difference_amount is not None
+		else payment_entry.get_exchange_rate(),
+		"exchange_gain_loss": d.difference_amount,
 	}
 
 	if d.voucher_detail_no: