[loaders-] handle exceptions in filetype guess

[midichef]

Exceptions during filetype guessing are usually invisible, and only show up when running vd --debug. This PR handles a couple of these usually invisible exceptions, to clean up the debug status log.

Empty files cause empty messages for a few filetypes: echo -n '' |vd --debug

guess_jsonla: 
guess_json: 
guess_csv: 

And a JSON file causes an error in the JSONLA guesser: echo '[\n{"id": 1}\n]' |vd --debug

guess_jsonla: Expecting value: line 2 column 1 (char 2)```

[saulpw]

We don't necessarily have to log any errors, even in debug output; maybe should we just remove that instead of trying to handle all exceptions in each guesser? I only put it there because it seemed like it would be handy for when someone was trying to debug why the file type wasn't being guessed correctly for some file, or when writing or updating a guesser. But maybe it's just noisy for the vast majority of times we use --debug.

[midichef]

The error log is useful for me at the moment. I'm using --debug to check for errors in file guessing, as I try to make a binary version of RepeatFile. That's how I noticed the errors in these corner cases. So it is handy for now.