[FIX] stock: use default lang when no partner in deliveryslip

Step to reproduce:

1. create a product
2. duplicate it and change its translation (but DO NOT change the product name)
3. create a transfer for that new product without a contact
4. print delivery slip

Bug:
the db's product name is used instead of the translated name
(i.e. "original product name (copy)")

FIX:
when partner id is not set in picking, then default to the user's language

opw-3141202

closes odoo/odoo#116610

X-original-commit: e56b955fbd7963709b9547eb50d97cf105f9d430
Signed-off-by: Tiffany Chang <tic@odoo.com>
Signed-off-by: Walid Hanniche (waha) <waha@odoo.com>

addons/stock/report/report_deliveryslip.xml

@@ -3,7 +3,7 @@
     <template id="report_delivery_document">
         <t t-call="web.html_container">
             <t t-call="web.external_layout">
-                <t t-set="o" t-value="o.with_context(lang=o.partner_id.lang)" />
+                <t t-set="o" t-value="o.with_context(lang=o.partner_id.lang or o.env.lang)" />
                 <t t-set="partner" t-value="o.partner_id or (o.move_ids and o.move_ids[0].partner_id) or False"/>
 
                 <t t-set="address">
@@ -273,7 +273,7 @@
 
     <template id="report_deliveryslip">
         <t t-foreach="docs" t-as="o">
-            <t t-call="stock.report_delivery_document" t-lang="o.partner_id.lang"/>
+            <t t-call="stock.report_delivery_document" t-lang="o.partner_id.lang or o.env.lang"/>
         </t>
     </template>
 </odoo>