added a helpful assert to the queue code

Now, instead of failing later when it tries to use it, it fails
immediately when it fails to get a new message to send.

git-svn-id: https://robotics.mvla.net/svn/frc971/2013/trunk/src@4159 f308d9b7-e957-4cde-b6ac-9a88185e7312
1 file changed