res_pjsip_outbound_registration: Fix reference leak.

Every time a registration started, sip_outbound_registration_response_cb bumps 
the ref count on client_state then pushes a handle_registration_response task.  
handle_registration_response never unreffed it though.  So every time a 
registration goes out, the ref count goes up by one.

This patch adds the unreffs to handle_registration_response.

Tested-by: George Joseph

Review: https://reviewboard.asterisk.org/r/4303/
........

Merged revisions 430395 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@430396 65c4cc65-6c06-0410-ace0-fbb531ad65f3

res/res_pjsip_outbound_registration.c

@@ -462,7 +462,7 @@ static int handle_client_registration(void *data)
 	pjsip_regc_info info;
 	char server_uri[PJSIP_MAX_URL_SIZE], client_uri[PJSIP_MAX_URL_SIZE];
 
-	cancel_registration(client_state);
+	ao2_ref(client_state, -1);
 
 	if ((client_state->status == SIP_REGISTRATION_STOPPED) ||
 		(pjsip_regc_register(client_state->client, PJ_FALSE, &tdata) != PJ_SUCCESS)) {