prevent segfault if bad magic number is encountered.

internal_ao2_ref uses INTERNAL_OBJ which mzy report 'bad magic number', but
internal_ao2_ref continues on, causing segfault.

Although AO2_MAGIC number is checked by INTERNAL_OBJ before internal_ao2_ref is
called, A02_MAGIC is being destroyed (or a wrong pointer) by the time
internal_ao2_ref uses INTERNAL_OBJ.

internal_ao2_ref now returns -1 if INTERNAL_OBJ encouters a bad magic number.

(issue #17037)
Reported by: alecdavis
Patches:
      bug17037.diff.txt uploaded by alecdavis (license 585)
Tested by: alecdavis




git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@253490 65c4cc65-6c06-0410-ace0-fbb531ad65f3