Move render_options in filter after the error has been set

Experimental.
Move render_options in filter after the error has been set in order for an `doorkeeper_unauthorized_render_options` override to catch the response and present it to the user.

```
  def doorkeeper_unauthorized_render_options
    { json: { error: @error.description }}
  end
```

Also `@error` is too generic, should we change name to something more in scope?