Move adjustment of revision delete target in SpecialRevisiondelete to fix fatal

targetObj needs to be set correctly before accessing the RevisionList,
and trying to get the 'current'.  If not set correctly, then $title
given to RevisionList (and it's subclasses) is Special:Revisiondelete
and rev_page is 0. So nothing is found for 'current' and a fatal
error happens.

Follow-up to Id1baacb

Bug: 68566
Change-Id: Ic078af5417798db1b2900057dbf7514112e94b46
(cherry picked from commit 570b6bdffee3ef1a81cfc83f0fdb7d8a15ea77a6)
Merge "Move adjustment of revision delete target in SpecialRevisiondelete to fix fatal" into wmf/1.24wmf15