[FIX] purchase: Description is changed after quantity is modified if seller is set

TT36008

closes odoo/odoo#90056

X-original-commit: d696f070c6a0412236816a9f36ebba8b15ab0cf2
Signed-off-by: Arnold Moyaux <arm@odoo.com>

addons/purchase/models/purchase.py

@@ -1232,7 +1232,8 @@ class PurchaseOrderLine(models.Model):
 
         self.price_unit = price_unit
         product_ctx = {'seller_id': seller.id, 'lang': get_lang(self.env, self.partner_id.lang).code}
-        self.name = self._get_product_purchase_description(self.product_id.with_context(product_ctx))
+        if seller.product_name:
+            self.name = self._get_product_purchase_description(self.product_id.with_context(product_ctx))
 
     @api.onchange('product_id', 'product_qty', 'product_uom')
     def _onchange_suggest_packaging(self):