MDEV-20578 Got error 126 when executing undo undo_key_delete
upon Aria crash recovery

The crash happens in this scenario:
- Table with unique keys and non unique keys
- Batch insert (LOAD DATA or INSERT ... SELECT) with REPLACE
- Some insert succeeds followed by duplicate key error

In the above scenario the table gets corrupted.

The bug was that we don't generate any undo entry for the
failed insert as the whole insert can be ignored by undo.
The code did however not take into account that when bulk
insert is used, we would write cached keys to the file on
failure and undo would wrongly ignore these.

Fixed by moving the writing of the cache keys after we write
the aborted-insert event to the log.