Inbound activity emails - don't fire hook if activity processing failed

In CRM_Utils_Mail_EmailProcessor there is code to process emails as activities.

In event that the Activity processing fails, we should not then fire

            CRM_Utils_Hook::emailProcessor('activity', $params, $mail, $result);

If an email is inbound which triggers Activity API to reject it (eg, Google Drive "Share document" link which contains a <script> tag), then this may prevent processing of further emails.

Trivial fix is to move the hook call inside the block which ensures that the Activity,create API call was successful.