Don't panic while searching gateway

[ackintosh]

search_gateway() panics because of attohttpc::get() would panics with something invalid urls.

This PR makes search_gateway() log errors instead of panic so that users identify the cause of errors.

[ackintosh]

@sbstp Thank you for merging this! I would appreciate it if you cut a new release. 🙂

[sbstp]

done