Check if a previous run left an inconsistent state behind.
The check is right before trying to push a new state as then
all information is available, like commit message and tag
name.

This is still only a band-aid. If gnumbd is down for a
longer period, an unprocessed commit won't be found, but
the push attempt will still fail.

Review URL: https://codereview.chromium.org/1887583002

Cr-Commit-Position: refs/heads/master@{#35437}