Problem :
---------
This is a regression of bug-19138298. During purge, if
btr_pcur_restore_position fails, we set found_clust to FALSE
so that it can find a possible clustered index record in future
calls for the same undo entry. This, however, overwrites the
old_rec_buf while initializing pcur again in next call.

The leak is reproducible in local environment and with the
test provided along with bug-19138298.

Solution :
----------
If btr_pcur_restore_position() fails close the cursor.
Reviewed-by: Marko Makela <Marko.Makela@oracle.com>
Reviewed-by: Annamalai Gurusami <Annamalai.Gurusami@oracle.com>

RB: 9074