[FIX] stock: get product qty based on location and warehouse

When getting the available quantity of a product, it is possible to
specify the warehouse and/or the location in the context. However,
it does not correctly work. For instance, if we provide the stock
location ID (8) and the warehouse ID (1): we first use the view
location of the warehouse, and we then get the intersection between
this view location and the provided locations: nothing. In such case,
we should keep the stock location. Few other examples are given in
the test.

OPW-3450169

closes odoo/odoo#134680

Signed-off-by: William Henrotin (whe) <whe@odoo.com>
Co-authored-by: Simon Schmid <simon.schmid@braintec.com>