LeftAndMain::handleRequest() misusing ValidationException

[emteknetnz]

LeftAndMain::handleRequest() is catching ValidationException then using $e->getMessage() and using that as the error message for the HTTP response, which could be then displayed to a CMS author.

ValidationExceptions are intended for developers and not for CMS authors. What is really should be happening is the ValidationResult is extracted from the ValidationException and its message is shown.

However we don't actually currently know what contexts this code path is even triggered, and there may be a reason which makes doing this difficult e.g. there are multiple errors in the Validation result but we should only display the first message.

Acceptance criteria

• LeftAndMain::handleRequest() no longer relies on the exception message
• The condition that adds context to the validation exception message is removed, as that information should always be provided where available.