strncmp is better than strpos

Summary: no need to get all O(N) up in this when we can do constant time of "8"

Test Plan: arc lint

Reviewers: vrana, epriestley

Reviewed By: vrana

CC: aran, Korvin

Maniphest Tasks: T891

Differential Revision: https://secure.phabricator.com/D3271

src/applications/auth/oauth/provider/PhabricatorOAuthProviderPhabricator.php

@@ -105,7 +105,7 @@ extends PhabricatorOAuthProvider {
 
   public function setUserData($data) {
     // legacy conditionally strip shield. see D3265 for discussion.
-    if (strpos($data, 'for(;;);') === 0) {
+    if (strncmp($data, 'for(;;);', 8) === 0) {
       $data = substr($data, 8);
     }
     $data = idx(json_decode($data, true), 'result');