Do not use OFX balance statement if the balance date is not the statement end date

The bank can put a balance for the statement at a different date than the end
date of the statement. But for Tryton the end balance must be the balance at
the end of the statement.

Closes #13982
(grafted from 46dc70e63342ec41efdf55f2c9e77f2ec27882a8)

--HG--
branch : 7.0

modules/account_statement_ofx/account.py

@@ -57,14 +57,17 @@ class StatementImport(metaclass=PoolMeta):
             raise ImportStatementError(
                 gettext('account_statement_ofx.msg_import_no_statement'))
         try:
-            statement.date = ofx_account.statement.balance_date.date()
+            statement.date = ofx_account.statement.end_date.date()
         except AttributeError:
             pass
         total_amount = sum(
             t.amount for t in ofx_account.statement.transactions)
         statement.total_amount = total_amount
-        statement.start_balance = ofx_account.statement.balance - total_amount
-        statement.end_balance = ofx_account.statement.balance
+        if (ofx_account.statement.end_date
+                == ofx_account.statement.balance_date):
+            statement.start_balance = (
+                ofx_account.statement.balance - total_amount)
+            statement.end_balance = ofx_account.statement.balance
         statement.number_of_lines = len(ofx_account.statement.transactions)
         return statement