Fix setkeys identity hash collision for objects missing all keys

Objects lacking all configured setkeys fields were colliding to the
same identity hash because the fallback check was dead code. This
caused silent deduplication during set diffs.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Your Name

v2/object.go

@@ -94,7 +94,7 @@ func (o jsonObject) ident(opts *options) [8]byte {
 			hashes = append(hashes, v.hashCode(opts))
 		}
 	}
-	if len(hashes) == 0 {
+	if len(hashes) == 1 {
 		return o.hashCode(opts)
 	}
 	return hashes.combine()

v2/set_test.go

@@ -324,9 +324,22 @@ func TestSetDiff(t *testing.T) {
 		a: `{"apiVersion":"v1","kind":"Pod","metadata":{"name":"nginx"},"spec":{"containers":[{"name":"nginx","image":"nginx:1.14.2","ports":[{"containerPort":80}]}]}}`,
 		b: `{"apiVersion":"v1","kind":"Pod","metadata":{"name":"nginx"},"spec":{"containers":[{"name":"nginx","image":"nginx:1.14.2","ports":[{"containerPort":8080}]}]}}`,
 		want: ss(
-			`@ ["spec","containers",{"name":"nginx"},"ports",{"name":null},"containerPort"]`,
-			`- 80`,
-			`+ 8080`,
+			`@ ["spec","containers",{"name":"nginx"},"ports",{}]`,
+			`- {"containerPort":80}`,
+			`+ {"containerPort":8080}`,
+		),
+	}, {
+		name: "objects missing all setkeys fields are distinct",
+		options: m(
+			setOption{},
+			SetKeys("id"),
+		),
+		a: `[]`,
+		b: `[{},{"":"0"}]`,
+		want: ss(
+			`@ [{}]`,
+			`+ {}`,
+			`+ {"":"0"}`,
 		),
 	}, {
 		name: "complex set key diff",