Audit ast_pjsip_rdata_get_endpoint() usage for ref leaks.

Audit ast_pjsip_rdata_get_endpoint() usage for ref leaks.

Valgrind found some memory leaks associated with
ast_pjsip_rdata_get_endpoint().  The leaks would manifest when sending
responses to OPTIONS requests, processing MESSAGE requests, and
res_pjsip supplements implementing the incoming_request callback.

* Fix ast_pjsip_rdata_get_endpoint() endpoint ref leaks in
res/res_pjsip.c:supplement_on_rx_request(),
res/res_pjsip/pjsip_options.c:send_options_response(),
res/res_pjsip_messaging.c:rx_data_to_ast_msg(), and
res/res_pjsip_messaging.c:send_response().

* Eliminated RAII_VAR() use with ast_pjsip_rdata_get_endpoint() in
res/res_pjsip_nat.c:nat_on_rx_message().

* Fixed inconsistent but benign return value in
res/res_pjsip/pjsip_options.c:options_on_rx_request().

Review: https://reviewboard.asterisk.org/r/4511/

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/13@433222 65c4cc65-6c06-0410-ace0-fbb531ad65f3