mac/rlz: Correctly check for fd existence

Found while looking at this file for http://crbug.com/143950, but
I don't think this causes that bug.

BUG=143950

Review URL: https://chromiumcodereview.appspot.com/10827449

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@152616 0039d316-1c4b-4281-b951-d872f2087c98

rlz/mac/lib/rlz_value_store_mac.mm

@@ -296,7 +296,7 @@
 }
 
 void RecursiveCrossProcessLock::ReleaseLock() {
-  if (file_lock_) {
+  if (file_lock_ != -1) {
     ignore_result(HANDLE_EINTR(flock(file_lock_, LOCK_UN)));
     ignore_result(HANDLE_EINTR(close(file_lock_)));
     file_lock_ = -1;