X509_NAME_cmp fix for empty name

CLA: trivial

Fixes #21156

Reviewed-by: Todd Short <todd.short@me.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from #21155)

(cherry picked from commit ec59752)

crypto/x509/x509_cmp.c

@@ -277,11 +277,11 @@ int X509_NAME_cmp(const X509_NAME *a, const X509_NAME *b)
     if (ret == 0 && a->canon_enclen == 0)
         return 0;
 
-    if (a->canon_enc == NULL || b->canon_enc == NULL)
-        return -2;
-
-    if (ret == 0)
+    if (ret == 0) {
+        if (a->canon_enc == NULL || b->canon_enc == NULL)
+            return -2;
         ret = memcmp(a->canon_enc, b->canon_enc, a->canon_enclen);
+    }
 
     return ret < 0 ? -1 : ret > 0;
 }