Fixes#1727.
With the server down, apply migrations 0245 and 0246. 0246 will remove
the pub_date column, so it's essential that the previous migrations
ran correctly to copy data before running this.
It's not clear to me how this is intended to work in Mattermost's
system in that they don't document this behavior, but some users have
`null` as their list of teams, and presumably are not meant to be
included in any team at all.