Bug 1339617 - move GetClosure call prior to canceling timer; r=mayhemer

Some recent work on timers changed how we handle callbacks and
associated closure data: prior to these changes, canceling timers would
not null out associated closure data, so calling GetClosure() on a timer
after canceling it would return what you had put in.  After these
changes, however, GetClosure() after cancellation would retrieve a null
value, causing anything that assumed non-nullness to crash.  The simple
fix is to move the GetClosure() call prior to Cancel()'ing the timer.

netwerk/cache/nsDeleteDir.cpp

@@ -80,10 +80,10 @@ nsDeleteDir::Shutdown(bool finishDeleting)
     for (int32_t i = gInstance->mTimers.Count(); i > 0; i--) {
       nsCOMPtr<nsITimer> timer = gInstance->mTimers[i-1];
       gInstance->mTimers.RemoveObjectAt(i-1);
-      timer->Cancel();
 
       nsCOMArray<nsIFile> *arg;
       timer->GetClosure((reinterpret_cast<void**>(&arg)));
+      timer->Cancel();
 
       if (finishDeleting)
         dirsToRemove.AppendObjects(*arg);