Apply same fix for SQL_ROLLBACK_TO_SAVEPOINT as for SQL_ROLLBACK
Apply same fix for SQL_ROLLBACK_TO_SAVEPOINT as for SQL_ROLLBACK

The issue here is that some SQL Server errors cause an active
transaction to be rolled back automatically and unconditionally.
Sequel has no way to know about this, and so must guard against
the case where there is no active transaction when it tries to
rollback.

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