Fix memory leak in logger.

Fixed a memory leak discovered in the logger where a temporary string buffer
was not being freed.

(closes issue ASTERISK-22540)
Reported by: John Hardin
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Merged revisions 399513 from http://svn.asterisk.org/svn/asterisk/branches/11
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Merged revisions 399514 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@399515 65c4cc65-6c06-0410-ace0-fbb531ad65f3