Fix a memory leak in register_group_feature when attempting to register

a feature without specifying a group or feature to register.

(closes issue #13101)
Reported by: eliel
Patches:
      features.c.patch uploaded by eliel (license 64)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@131717 65c4cc65-6c06-0410-ace0-fbb531ad65f3