Before this commit, calling unpatch on an object that hasn't been patched before crashed (before reaching the code that handles the case by throwing an Error). This scenario is now properly handled. This commit also defines specific Error classes for the patch and unpatch faulty cases, so that they can be elegantly catched (in tests for example). closes odoo/odoo#68057 Signed-off-by: Géry Debongnie (ged) <ged@openerp.com>