Add checks to try to catch T92046
Somehow, revisions are getting added to the database without issue but
page_latest is being set to 0 rather than the newly-added revision ID.
Grepping through the code, the only places page_latest gets set are
WikiPage::insertOn() (which isn't relevant for an edit of an existing
page) and WikiPage::updateRevisionOn(). And the only relevant-looking
place WikiPage::updateRevisionOn() gets called seems to be
WikiPage::doEditContent(), which calls Revision::insertOn() just before
which *should* be setting the mId on the revision object.
Since there's no obvious bug in the code, let's add some checks to make
sure that the revision ID isn't 0. If we see exceptions being thrown, at
least we'll have narrowed down the places we need to look more deeply.
And if not (and the bug continues to be reported), we'll at least know
this part is working right.