(bug 44219) Avoid fatal errors when a revision doesn't exist in action=info

WikiPage::getRevision() and WikiPage::getOldestRevision() may return null
when a revision does not exist; catch this in InfoAction::pageInfo().

Change-Id: If141213aedfe7c55e935105abf4415b6feced57c
Merge "(bug 44219) Avoid fatal errors when a revision doesn't exist in action=info"