Ensure REF_DEBUG records entrys for attempts to ao2_ref an invalid object

This change ensures that __ao2_ref_debug writes to ref_log when given a
non-NULL pointer to an invalid ao2 object.  This is to ensure that we
record any attempt manipulate references of already freed objects.

ASTERISK-23948 #close
Reported by: Corey Farrell
Review: https://reviewboard.asterisk.org/r/3677/
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Merged revisions 417500 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 417505 from http://svn.asterisk.org/svn/asterisk/branches/11
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Merged revisions 417509 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@417511 65c4cc65-6c06-0410-ace0-fbb531ad65f3