[FIX] web: BasicModel: send correct context

... when reading and writing on a record (especially inside lists).

Before this rev., the context sent when reading a record, and when
writing records inside lists (editable list views) wasn't correct.
This caused an issue in Sales > Products (variant activated) >
open a product with variants > click on variant prices > edit the
prices of a variant: the value wasn't saved correctly (because the
inverse function requires 'active_id' to be in the context and it
wasn't the case).