test_linkedlists: Fix memory leak

(issue ASTERISK-22467)
Reported by: Corey Farrell
Patches:
    test_linkedlists-1.8.patch uploaded by coreyfarrell (license 5909)
    test_linkedlists-11up.patch uploaded by coreyfarrell (license 5909)
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Merged revisions 401790 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 401791 from http://svn.asterisk.org/svn/asterisk/branches/11
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Merged revisions 401792 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@401793 65c4cc65-6c06-0410-ace0-fbb531ad65f3