fix problem with show_to_sign when more than one picking

ext/custom-addons/dp_custom/models/stock.py

@@ -64,9 +64,20 @@ class StockPicking(models.Model):
     @api.multi
     @api.depends('state', 'picking_signature')
     def _compute_show_to_sign(self):
+#        self.ensure_one()
         for picking in self:
             picking.show_to_sign = ''
-            if picking.picking_signature == '' or picking.picking_signature == None or len(self['picking_signature']) == 3012:
+            s_len = 0
+            try:
+                s_len = len(self['picking_signature'])
+            except:
+                pass
+            try:
+                s_len = len(picking.picking_signature)
+            except:
+                pass
+
+            if picking.picking_signature == '' or picking.picking_signature == None or s_len == 3012:
                 picking.show_to_sign = 'btn-primary'
 
     @api.multi