[cache][partial] Fix inverted err check.

Bug: 34965
Change-Id: I03fc807dae183ed978892662381c2f365d07825f
Reviewed-on: https://fuchsia-review.googlesource.com/c/jiri/+/392217
Commit-Queue: Nathan Mulcahey <nmulcahey@google.com>
Reviewed-by: Haowei Wu <haowei@google.com>
diff --git a/gitutil/git.go b/gitutil/git.go
index 7826e21..93b2c69 100644
--- a/gitutil/git.go
+++ b/gitutil/git.go
@@ -265,7 +265,7 @@
 		// This removes a `git rev-list -n 1 <rev>` which takes ~30 seconds for
 		// git partial-clones on `fuchsia/fuchsia`
 		var expectedRevision string
-		if _, err := hex.DecodeString(rev); len(rev) == 40 && err != nil {
+		if _, err := hex.DecodeString(rev); len(rev) == 40 && err == nil {
 			expectedRevision = rev
 		}
 		if expectedRevision == "" {