fix bug in healthCheckConn.update when healthErr is nil
fix bug in healthCheckConn.update when healthErr is nil

Signed-off-by: Michael Demmer <4b836671cce77b1b2fbe63e5b2a1661879d8af44@slack-corp.com>

dcadevil/vitess,alainjobart/vitess,mahak/vitess,alainjobart/vitess,HubSpot/vitess,alainjobart/vitess,enisoc/vitess,mahak/vitess,enisoc/vitess,HubSpot/vitess,vitessio/vitess,mahak/vitess,vitessio/vitess,tinyspeck/vitess,davygeek/vitess,vitessio/vitess,dcadevil/vitess,davygeek/vitess,vitessio/vitess,enisoc/vitess,mahak/vitess,vitessio/vitess,alainjobart/vitess,davygeek/vitess,dcadevil/vitess,tinyspeck/vitess,HubSpot/vitess,tinyspeck/vitess,alainjobart/vitess,HubSpot/vitess,dcadevil/vitess,dcadevil/vitess,alainjobart/vitess,tinyspeck/vitess,alainjobart/vitess,HubSpot/vitess,tinyspeck/vitess,alainjobart/vitess,davygeek/vitess,HubSpot/vitess,mahak/vitess,davygeek/vitess,vitessio/vitess,enisoc/vitess,dcadevil/vitess,enisoc/vitess,mahak/vitess,dcadevil/vitess,vitessio/vitess,mahak/vitess,HubSpot/vitess,enisoc/vitess,vitessio/vitess,mahak/vitess,davygeek/vitess,davygeek/vitess,tinyspeck/vitess,HubSpot/vitess,tinyspeck/vitess,enisoc/vitess