json generator bug if using cache

[nikophil]

JSON generation process is not smart enough to realize that it doesn't need to rebuild everything.

It should be as simple as: if you can't find an Environment for a file (or maybe there is a better way to know if it was parsed, like using the ParseQueue, which has the list of files that needed to be parsed), then skip - the JSON should still be there and should still be up to date (I suppose we could throw an error if we find that the JSON file is missing for some reason)