[PATCH] Thread::Queue 2.09

Explicitly check for undef in args because some versions of
looks_like_number(undef) return true:
  http://www.nntp.perl.org/group/perl.cpan.testers/2008/05/msg1534197.html

• [PATCH] Thread::Queue 2.09 by Jerry D. Hedden
• Re: [PATCH] Thread::Queue 2.09 by Rafael Garcia-Suarez