res_pjsip_registrar.c: Miscellaneous cleanup in rx_task().

* Fix variable shadowing of 'updated' by renaming it to 'contact_update'.

* Checked 'contact_update' for ast_sorcery_copy() failure.

* Removed silly use of RAII_VAR() for 'contact_update'.


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/12@410995 f38db490-d61c-443f-a65b-d21fe96a405b