If malloc returns NULL, we need to return NULL immediately or

else Asterisk will crash when attempting to dereference the NULL
pointer

(closes issue #13858)
Reported by: eliel
Patches:
      astmm.c.patch uploaded by eliel (license 64)



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@157632 65c4cc65-6c06-0410-ace0-fbb531ad65f3