Ensure overlapping hold flags do not conflict

When changing between different modes of hold, the flags were not being
cleared out properly causing a failure to change hold states.

(closes issue ASTERISK-19919)
Patch-by: Morten Tryfoss
Reported-by: Morten Tryfoss
........

Merged revisions 368586 from http://svn.asterisk.org/svn/asterisk/branches/1.8
........

Merged revisions 368587 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@368588 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -9037,6 +9037,9 @@ static void change_hold_state(struct sip_pvt *dialog, struct sip_request *req, i
 	}
 	/* No address for RTP, we're on hold */
 
+	/* Ensure hold flags are cleared so that overlapping flags do not conflict */
+	ast_clear_flag(&dialog->flags[1], SIP_PAGE2_CALL_ONHOLD);
+
 	if (sendonly == 1)	/* One directional hold (sendonly/recvonly) */
 		ast_set_flag(&dialog->flags[1], SIP_PAGE2_CALL_ONHOLD_ONEDIR);
 	else if (sendonly == 2)	/* Inactive stream */