[v18] Check err != nil before calling err.Error() in tbot db tunnel service (#64574)

* Check err != nil before calling err.Error() in tbot db tunnel service

If the local proxy Start() method returns a nil error, we do a nil
pointer deference. This does a check first.

* fmt

* Report unhealthy even if err is nil

Author: rob-picard-teleport

lib/tbot/services/database/tunnel_service.go

@@ -241,7 +241,11 @@ func (s *TunnelService) Run(ctx context.Context) error {
 	case <-ctx.Done():
 		return nil
 	case err := <-errCh:
-		s.statusReporter.ReportReason(readyz.Unhealthy, err.Error())
+		if err != nil {
+			s.statusReporter.ReportReason(readyz.Unhealthy, err.Error())
+		} else {
+			s.statusReporter.Report(readyz.Unhealthy)
+		}
 		return trace.Wrap(err, "local proxy failed")
 	}
 }