[FIX] stock: return picking wizard handles one picking at a time

We force the user to select only one picking at a time. The reason is that we
can choose the number of products to return for every picking, so it does not
make sense to group the returns in one picking.

opw-640030

addons/stock/wizard/stock_return_picking.py

@@ -63,6 +63,9 @@ class stock_return_picking(osv.osv_memory):
         result1 = []
         if context is None:
             context = {}
+        if context and context.get('active_ids', False):
+            if len(context.get('active_ids')) > 1:
+                raise osv.except_osv(_('Warning!'), _("You may only return one picking at a time!"))
         res = super(stock_return_picking, self).default_get(cr, uid, fields, context=context)
         record_id = context and context.get('active_id', False) or False
         pick_obj = self.pool.get('stock.picking')