Add handling of linter messages when no linters for a file type exist (r...

...esets the linter indicator).

Fixes #66.
In this case, this does work without the wrapping - but I found that jQuery will convert `triggerHandler("fatalError", null)` into this call: `handler(evt, undefined)`. At least, that is what my preliminary testing showed.

Will migrate back to `null` since it works in this case, though.