Pass the file contents instead of the file path to phutil_json_decode.

Summary: See D9681#22.

Test Plan: Created an empty `.git/arc/config` file... no exception was thrown.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9704

src/workingcopyidentity/ArcanistWorkingCopyIdentity.php

@@ -311,7 +311,8 @@ final class ArcanistWorkingCopyIdentity {
             $local_path));
 
         try {
-          return phutil_json_decode($local_path);
+          $json = Filesystem::readFile($local_path);
+          return phutil_json_decode($json);
         } catch (PhutilJSONParserException $ex) {
           throw new PhutilProxyException(
             pht("Failed to parse '%s' as JSON.", $local_path),