Fix redesign branch repository controller for Subversion

Summary: We access this variable, but may never initialize it.

Test Plan: Viewed SVN repository.

Reviewers: btrahan, chad

Reviewed By: chad

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D13544

src/applications/diffusion/controller/DiffusionRepositoryController.php

@@ -628,6 +628,7 @@ final class DiffusionRepositoryController extends DiffusionController {
     $header->addActionLink($button);
     $browse_panel->setHeader($header);
 
+    $locate_panel = null;
     if ($repository->canUsePathTree()) {
       Javelin::initBehavior(
         'diffusion-locate-file',