Don't log update errors (e.g. SQLITE_CONSTRAINT on duplicate insert) when _logsErrors is NO

My use case which motivates this patch is being able to INSERT a contact which may already be in the database. If I see an error after a INSERT update, I can safely ignore the error if it was SQLITE_CONSTRAINT. (In this case I don't want it NSLogged as an error, as there can be hundreds of these errors in a row).

Cheers!
Marcus