[FIX] stock: unlink zero quants

If you create a quant through the inventory mode of the list view and
you don't set a quantity, the quantity is null and the quant isn't
unlinked by _unlink_zero_quants.

Also consider null quantity as 0.

We don't have the issue for the reserved_quantity field since this one
is not nullable.

closes odoo/odoo#48005

X-original-commit: 08e428458aa545b3602c56b6866a447126cf8825
Signed-off-by: Simon Lejeune (sle) <sle@openerp.com>

addons/stock/models/stock_quant.py

@@ -507,7 +507,7 @@ class StockQuant(models.Model):
         """
         precision_digits = max(6, self.sudo().env.ref('product.decimal_product_uom').digits * 2)
         # Use a select instead of ORM search for UoM robustness.
-        query = """SELECT id FROM stock_quant WHERE round(quantity::numeric, %s) = 0 AND round(reserved_quantity::numeric, %s) = 0;"""
+        query = """SELECT id FROM stock_quant WHERE (round(quantity::numeric, %s) = 0 OR quantity IS NULL) AND round(reserved_quantity::numeric, %s) = 0;"""
         params = (precision_digits, precision_digits)
         self.env.cr.execute(query, params)
         quant_ids = self.env['stock.quant'].browse([quant['id'] for quant in self.env.cr.dictfetchall()])