If no number is specified in the SIP_HEADER dialplan function, then just use the first one. (issue #7854 reported by sxpert and issue #7863 reported by hristo)

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@41689 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -10909,9 +10909,13 @@ static int func_header_read(struct ast_channel *chan, char *function, char *data
 	}
 
 	AST_STANDARD_APP_ARGS(args, data);
-	sscanf(args.number, "%d", &number);
+	if (!args.number) {
-	if (number < 1)
 		number = 1;
+	} else {
+		sscanf(args.number, "%d", &number);
+		if (number < 1)
+			number = 1;
+	}
 
 	p = chan->tech_pvt;