Re: master 6aa04a5: * lisp/json.el (json-end-of-file): New error.

[Artur Malabarba <bruce.connor.am@gmail.com>]

> +(define-error 'json-end-of-file "End of file while parsing JSON"
> +  '(end-of-file json-error))

When this form is evaluated, I get the following error:
     error: "Attempt to modify read-only object", (error)

Looking into `define-error', this happens when it tries to `apply'
`nconc' on the result of the `mapcar', which is this:
    ((end-of-file end-of-file error) (json-error json-error error))


I think it may be a bug in `define-error', where that nconc should be
an append. Otherwise, nconc tries to destructively change the list it
gets from (get parent 'error-conditions), which I'm guessing shouldn't
be changed.
I may just be wrong, though. `git blame' reveal this function has
existed in this form since 2013...