[FIX] stock: unlink scrap on cancel

from f5e99060, a scrap order was unlink
when clicking the discard button in the insufficient quantity wizard.
This lead to a access error when the wizard was closed on the scrap order
form view. The form view was reloaded on a deleted record.

This commit adds a context key that prevent the unlink if the scrap order
was validated from the scrap form view

Task : 2043136

addons/stock/views/stock_scrap_views.xml

@@ -25,7 +25,7 @@
             <field name="arch" type="xml">
                 <form string="Scrap">
                     <header>
-                        <button name="action_validate" states="draft" string="Validate" type="object" class="oe_highlight"/>
+                        <button name="action_validate" states="draft" string="Validate" type="object" class="oe_highlight" context="{'not_unlink_on_discard': True}"/>
                         <field name="state" widget="statusbar" statusbar_visible="draft,done" />
                     </header>
                     <sheet>

addons/stock/wizard/stock_warn_insufficient_qty.py

@@ -37,4 +37,7 @@ class StockWarnInsufficientQtyScrap(models.TransientModel):
 
     def action_cancel(self):
         # FIXME in master: we should not have created the scrap in a first place
-        return self.scrap_id.sudo().unlink()
+        if self.env.context.get('not_unlink_on_discard'):
+            return True
+        else:
+            return self.scrap_id.sudo().unlink()