[FIX] Remove bad undefined value returned instead of a real promise.

[FIX] Remove bad undefined value returned instead of a real promise.

Thanks Valentin ! I didn't paid attention to this potential problem.
I guess we'll have to review the usage of promises as openerp callback
return value because any addons adding a callback could potentially break
the promises.

bzr revid: fme@openerp.com-20111011135820-v1lx6uj1siqbq7m6