[FIX] stock: print non unit UoM products labels

Steps to reproduces:
- Create two products one with UoM units and the other grams
- Create and confirm an SO with these two products
- Set quantities and validate the transfer
- Click "Print labels"

Bug:
only products with UoM units are printed because "quantity_by_product"
is overwritten with only those products

opw-3658993

closes odoo/odoo#151236

X-original-commit: d3c3e2013bd3ef2fe78c8f27b15daeb633c4d9a0
Signed-off-by: William Henrotin (whe) <whe@odoo.com>
Signed-off-by: Walid Hanniche (waha) <waha@odoo.com>

addons/stock/wizard/product_label_layout.py

@@ -42,6 +42,8 @@ class ProductLabelLayout(models.TransientModel):
                         custom_barcodes[line.product_id.id].append((line.lot_id.name or line.lot_name, int(line.quantity)))
                         continue
                     quantities[line.product_id.id] += line.quantity
+                else:
+                    quantities[line.product_id.id] = 1
             # Pass only products with some quantity done to the report
             data['quantity_by_product'] = {p: int(q) for p, q in quantities.items() if q}
             data['custom_barcodes'] = custom_barcodes