Keep 0 valued change approval records

Scanning through the Gerrit1 data for review.source.android.com, about
26.2% of the change approval records are 0.  In pretty much every case
this is a user trying to indicate they want to watch the change as an
interested reviewer.  We might as well keep those records in place and
reuse them later to help display user dashboards.

Signed-off-by: Shawn O. Pearce <sop@google.com>
6 files changed