fix a seg fault in this application if no context paramater is given

(issue #7571)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@38118 65c4cc65-6c06-0410-ace0-fbb531ad65f3

apps/app_directed_pickup.c

@@ -83,7 +83,7 @@ static int pickup_exec(struct ast_channel *chan, void *data)
 			*context++ = '\0';
 
 		/* If the context is the pickup mark, iterate through all channels finding the right origin one */
-		if (!strcmp(context, PICKUPMARK)) {
+		if (context && !strcmp(context, PICKUPMARK)) {
 			while ((origin = ast_channel_walk_locked(origin))) {
 				if (origin) {
 					tmp2 = pbx_builtin_getvar_helper(origin, PICKUPMARK);