test_linkedlists: Fix memory leak

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)
........

Merged revisions 401790 from http://svn.asterisk.org/svn/asterisk/branches/1.8
........

Merged revisions 401791 from http://svn.asterisk.org/svn/asterisk/branches/11
........

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