[5.5] Run after-callbacks even if a callback event failed

[themsaid]

Currently if you use exec(), or command() an after-callback will run even if the command itself threw an exception since the command runs in a sub-process.

However when you use a callback event, any exception in the callback will prevent the script from continuing and thus cause the after-callbacks to never fire.

This PR fixes this issue by ensuring the after-callbacks are called even if the callback event failed.