catch and log payload handling errors
It doesn't look like you are maintaining slack-client any longer, but my bot receives killer channel_archive messages from Slack, I haven't caught the message itself, but here is the result:
PHP Fatal error: Uncaught ErrorException: Illegal string offset 'id' in /home/kip/php-kip/vendor/coderstephen/slack-client/src/RealTimeClient.php:406
This PR attempts to ameliorate by catching and logging errors thrown while handling payloads.
I'd avoid Throwable if possible, since the library is currently targeting PHP 5.5+. We could boost it to PHP 7+ only as a new version, but we can't because there's some known compatibility issues between the websocket library being used and PHP 7.
I have changed the PR to use \Exception instead. I am using a fork of devristo/phpws with updated react/socket and react/socket-client dependencies https://github.com/nopolabs/phpws/commit/40c0be66747ff982f287bc9f35a34ca67d72eb19 and haven't had any troubles.