Ignore empty errors on postgres upsert fail
Ignore empty errors on postgres upsert fail

- Postgres's behavior when there is no update is that there is an
  ErrNoRows thrown back, which we can safely ignore since the only time
  this can happen in postgres's case is under this circumstance since
  there's no race unlike the mysql upsert code.
- Fix #84

volatiletech/sqlboiler,nullbio/sqlboiler,vattle/sqlboiler,volatiletech/sqlboiler