[FIX] stock: empty state

- Update view with external_id=stock.view_move_picking_tree and remove
  editable attribute on the tree view.
- Create a new picking
- Add a line (form view will open) and click on "Save and close"

=> A traceback show up since 'scrapped' was not in the form view.

- The picking location fields become readonly, and the status bar
  disappears
- Save the picking

=> Error: "creation/update: a mandatory field is not correctly set :
   [object with reference: location_id - location.id]"

Courtesy of @benwillig

Closes #17738
opw-748353

addons/stock/models/stock_picking.py

@@ -325,11 +325,11 @@ class Picking(models.Model):
                 .filtered(lambda move: move.state not in ['cancel', 'done'])\
                 .sorted(key=lambda move: (move.state == 'assigned' and 2) or (move.state == 'waiting' and 1) or 0)
             if self.move_type == 'one':
-                self.state = moves_todo[0].state
+                self.state = moves_todo[0].state or 'draft'
             elif moves_todo[0].state != 'assigned' and any(x.partially_available or x.state == 'assigned' for x in moves_todo):
                 self.state = 'partially_available'
             else:
-                self.state = moves_todo[-1].state
+                self.state = moves_todo[-1].state or 'draft'
 
     @api.one
     @api.depends('move_lines.priority')

addons/stock/views/stock_move_views.xml

@@ -157,6 +157,7 @@
                 <header>
                         <field name="state" widget="statusbar"/>
                 </header>
+                <field name="scrapped" invisible="1"/>
                 <group>
                     <group string="#Products">
                         <field name="product_id"/>