It's possible that MDL conflict handling code is called more
than once for a transaction when:
- it holds more than one conflicting MDL lock
- reschedule_waiters() is executed,
which results in repeated attempts to BF-abort already aborted
transaction.
In such situations, it might be that BF-aborting logic sees
a partially rolled back transaction and erroneously decides
on future actions for such a transaction.

The specific situation tested and fixed is when a SR transaction
applied in the node gets BF-aborted by a started TOI operation.
It's then caught with the server transaction already rolled back,
but with no MDL locks yet released. This caused wrong state
detection for such a transaction during repeated MDL conflict
handling code execution.
Signed-off-by: Julius Goryavsky <julius.goryavsky@mariadb.com>