Stat error and log handling in a single place

[diocas]

Method _file_model is used to create a specific JSON response that describes a model and it's used in at least 3 cases. Reading, saving, and creating a new file (which is actually calling a save() method).
So this calls for a bigger refactor than just one place. I suggest we resolve this in a separate issue.

Originally posted by @piotrWichlinskiSoftwaremind in #213 (comment)