[FIX] mrp: default sequence on bom line

To avoid null sequence
Fixes #6074

addons/mrp/mrp.py

@@ -421,6 +421,7 @@ class mrp_bom_line(osv.osv):
         'product_rounding': lambda *a: 0.0,
         'type': lambda *a: 'normal',
         'product_uom': _get_uom_id,
+        'sequence': 1,
     }
     _sql_constraints = [
         ('bom_qty_zero', 'CHECK (product_qty>0)', 'All product quantities must be greater than 0.\n' \