DEV: Skip DetectTranslation jobs for small action posts

[markvanlan]

This is an extension of this commit - 1c84ffe

We had a problem on a site where a bunch of jobs were enqueued to detect the language of the same small post. Not sure what triggered this, but it caused an endless stream of revised message bus messages to the client, causing network requests to flood the server and rate limit clients.

This does a super-safe job of

1. not enqueueing the process job for small/empty posts
2. returning early in the job if a post somehow made it through

[markvanlan]

Eh I thought this was still an issue. It shouldnt' be. But gosh enqueueing a job from a serializer that triggers a refresh, making the serializer run again potentially enqueueing the job again... spooky stuff here