[FIX] project: add misssing decorator on onchange method

The onchange should have the signature with `ids` instead of `id` for a proper
guess.
Without this, the method can not be overriden with an api.multi (the return
result is a list of dictionnary which is not understood by the ORM as a proper
return format).

Fixes #12856

addons/project/project.py

@@ -23,7 +23,7 @@ from datetime import datetime, date
 from lxml import etree
 import time
 
-from openerp import SUPERUSER_ID
+from openerp import SUPERUSER_ID, api
 from openerp import tools
 from openerp.addons.resource.faces import task as Task
 from openerp.osv import fields, osv
@@ -673,6 +673,7 @@ class task(osv.osv):
     def onchange_planned(self, cr, uid, ids, planned=0.0, effective=0.0):
         return {'value': {'remaining_hours': planned - effective}}
 
+    @api.cr_uid_ids_context
     def onchange_project(self, cr, uid, id, project_id, context=None):
         if project_id:
             project = self.pool.get('project.project').browse(cr, uid, project_id, context=context)