res_pjsip_outbound_registration.c: Move unref to a better place.

Move an unconditional unref of client_state so it doesn't look like it
could be used after the last ref has destroyed it.
........

Merged revisions 430902 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@430903 65c4cc65-6c06-0410-ace0-fbb531ad65f3