app_voicemail: Fix leaking config objects when msg_id doesn't match

(issues ASTERISK-22414)
Reported by: Corey Farrell
Patch:
    test_voicemail_api-leaks-11.patch uploaded by coreyfarrell (license 5909)
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Merged revisions 398281 from http://svn.asterisk.org/svn/asterisk/branches/11
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Merged revisions 398283 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@398284 65c4cc65-6c06-0410-ace0-fbb531ad65f3