jitterbuf: Fix memory leak on jitter buffer reset

(issue ASTERISK-22467)
Reported by: Corey Farrell
Patches:
    jitterbuf-jb_reset-leak-1.8.patch
    jitterbuf-jb_reset-leak-11up.patch
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Merged revisions 401786 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 401787 from http://svn.asterisk.org/svn/asterisk/branches/11
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Merged revisions 401788 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@401789 65c4cc65-6c06-0410-ace0-fbb531ad65f3