efl loop promises - cleare out promise data to null

efl loop promises - cleare out promise data to null

so there is something broken in the complect efl promise/loop promise
that the clear of promises on loop destroy is clearing
promises/futures that have already triggered (loop timer ones). i've
spent enough time figuring out that it is happening.
_efl_loop_timeout_del() simple doenst ensure the future in
pending_futures for that promise is removed from the list. getting the
future from the promise handle is an exercise in pain... so i'm not
continuing with that path and will just ignore it.

but for now filling the promise data with null at least means if the
menory is re-used after free it wont see garbage freed ptrs and get
nulls so its easier to track.