[UPD] In create method, use name field unless name_get

In create method, use name unless name_get to define res_name value.
In account.voucher model, the name_get return the amount, and we don't want this, we would like to get the name field.
@pedrobaeza : I think @hbrunn is rigth; It's better to add  a list of known bad models as 'account.voucher'.
We can have a model in the same time with the name field and name_get