Fixes a segfault occuring when performing attended transfer with FAXOPT(gateway)=yes

(closes issue ASTERISK-19184)
Reported by: Alexandr
........

Merged revisions 353962 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@353963 65c4cc65-6c06-0410-ace0-fbb531ad65f3

res/res_fax.c

@@ -2919,7 +2919,6 @@ static struct ast_frame *fax_gateway_framehook(struct ast_channel *chan, struct
 		if (!(details = find_details(chan))) {
 			ast_log(LOG_ERROR, "no FAX session details found on chan %s for T.38 gateway session, odd\n", ast_channel_name(chan));
 			ast_framehook_detach(chan, gateway->framehook);
-			details->gateway_id = -1;
 			return f;
 		}
 	}