gerrit: fix vet error

"go vet" now runs when the tests run, and errors on this test.

Change-Id: I239f23f51477530e4bda19793979e519fa371cdf
Reviewed-on: https://go-review.googlesource.com/80302
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/gerrit/gerrit_test.go b/gerrit/gerrit_test.go
index 0a91b30..b26c996 100644
--- a/gerrit/gerrit_test.go
+++ b/gerrit/gerrit_test.go
@@ -173,6 +173,9 @@
 	_, err := c.GetChange(context.Background(), "99999", QueryChangesOpt{
 		Fields: []string{"MESSAGES"},
 	})
+	if !hitServer {
+		t.Errorf("expected to hit test server, didn't")
+	}
 	if err != ErrChangeNotExist {
 		t.Errorf("expected ErrChangeNotExist, got %v", err)
 	}