res_pjsip_refer: Channel variable SIPREFERTOHDR not being set during blind transfer

The SIPREFERTOHDR channel variable is not being set on any channel when
performing a blind transfer using PJSIP. The 'refer->refer_to' was not
being set during a blind transfer.  Updated so the 'refer_to' is set to
the target uri on a blind transfer.

(closes issue ASTERISK-23502)
Reported by: John Bigelow
Review: https://reviewboard.asterisk.org/r/3445/
........

Merged revisions 412453 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@412454 65c4cc65-6c06-0410-ace0-fbb531ad65f3

res/res_pjsip_refer.c

@@ -680,6 +680,7 @@ static int refer_incoming_blind_request(struct ast_sip_session *session, pjsip_r
 	refer.context = context;
 	refer.progress = progress;
 	refer.rdata = rdata;
+	refer.refer_to = target;
 
 	switch (ast_bridge_transfer_blind(1, session->channel, exten, context, refer_blind_callback, &refer)) {
 	case AST_BRIDGE_TRANSFER_INVALID: