Fix order of start and base timestamps when switching to the wikitext editor

These were backwards which was triggering edit conflict detection for all users.

Fortunately for logged in users, if Revision::userWasLastToEdit was given a bad
timestamp (e.g. when we submitted here), it would just return true, suppressing
the conflict. It always showed a conflict for anonymous users however.

Bug: 56835
Change-Id: Ib07f965238ca96e17bf59b34da8a8e789954da61
Merge "Fix order of start and base timestamps when switching to the wikitext editor"