fixed RIPD-293 - return error when checking status of missing pathfinding request

https://ripplelabs.atlassian.net/browse/RIPD-293

I'm pretty sure this fixes the error where `path_find status` gets a weird "success" response when checking on a nonexistent pathfinding request, even though `path_find close` does return a reasonable error message. Looks like a simple typo in the original source.