Merged revisions 184078 via svnmerge from

https://origsvn.digium.com/svn/asterisk/branches/1.4

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  r184078 | mmichelson | 2009-03-24 17:34:45 -0500 (Tue, 24 Mar 2009) | 9 lines
  
  Change NULL pointer check to be ast_strlen_zero.
  
  The 'digit' variable is guaranteed to be non-NULL, so the if
  statement could never evaluate true. Changing to ast_strlen_zero
  makes the logic correct.
  
  This was found while reviewing ast_channel_ao2 code review.
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git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@184079 65c4cc65-6c06-0410-ace0-fbb531ad65f3