Merged revisions 79912 via svnmerge from

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

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r79912 | russell | 2007-08-17 16:01:43 -0500 (Fri, 17 Aug 2007) | 4 lines

Avoid a crash in the handling of DTMF based Caller ID.  It is valid for
ast_read to return NULL in the case that the channel has been hung up.
(crash reported by anonymouz666 on IRC in #asterisk-dev)

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git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@79913 65c4cc65-6c06-0410-ace0-fbb531ad65f3