[pat-auto-suggest] properly accept json for prefill-json #1278

I have some code that does that I use to fill data-pat-autosuggest:

options = {"prefill-json": [{"id: "john-snow", "text": "John Snow"]}
return json.dumps(options)

I had to change it like this:

options = {"prefill-json": json.dumps([{"id: "john-snow", "text": "John Snow"])}
return json.dumps(options)

otherwise I got the error:

SyntaxError: non-JSON data given to pat-autosuggest

The reason for the need for this change is that this line:

Tries to parse in to a Json something which is already an array.

I think that it would be convenient to check if prefillJson is a string before trying to apply JSON.parse.