fix: index error on Exchange Rate Revaluation creation

(cherry picked from commit bb279e368c)

erpnext/accounts/doctype/exchange_rate_revaluation/exchange_rate_revaluation.py

@@ -606,9 +606,9 @@ def get_account_details(
 	if account_balance and (
 		account_balance[0].balance or account_balance[0].balance_in_account_currency
 	):
-		account_with_new_balance = ExchangeRateRevaluation.calculate_new_account_balance(
+		if account_with_new_balance := ExchangeRateRevaluation.calculate_new_account_balance(
 			company, posting_date, account_balance
-		)
+		):
 			row = account_with_new_balance[0]
 			account_details.update(
 				{