Fix useRefetchable/fromData incompatibility

[benjamin-thomas]

Hello!

#628 introduced fromData, but it appeared to be incompatible with the useRefetchableFragment hook.

This change short-circuits the hook, similar to what was done in useFragment already.

For the background info: I encountered this error while trying to render some components on a "storybook-like" page.

The runtime error looked something like this:

    Invariant Violation: Relay: Expected to receive an object where `...TestRefetching_user` was spread, but the fragment reference was 
not found`. This is most likely the result of:                                                                                          
    - Forgetting to spread `TestRefetching_user` in `useRefetchableFragment()`'s parent's fragment.
    - Conditionally fetching `TestRefetching_user` but unconditionally passing useRefetchableFragment() prop to `TestRefetching_user`. I
...

The failing test captures the error I encountered faithfully

[tsnobip]

great fix @benjamin-thomas!

I'd just avoid using @obj and don't forget to update the CHANGELOG.md (add a # master section on top)

[tsnobip]

LGTM now!