[FIX] base_action_rule: Make sure model exists before trying to wrap hooks

In certain cases, before running an update unregistered models will try to
register hooks. Trying to wrap create and write on these will cause
AttributeError on model_obj which would be None

Signed-off-by: Sandy Carter <sandy.carter@savoirfairelinux.com>

addons/base_action_rule/base_action_rule.py

@@ -199,7 +199,7 @@ class base_action_rule(osv.osv):
         for action_rule in self.browse(cr, SUPERUSER_ID, ids):
             model = action_rule.model_id.model
             model_obj = self.pool.get(model)
-            if not hasattr(model_obj, 'base_action_ruled'):
+            if model_obj and not hasattr(model_obj, 'base_action_ruled'):
                 model_obj.create = self._wrap_create(model_obj.create, model)
                 model_obj.write = self._wrap_write(model_obj.write, model)
                 model_obj.base_action_ruled = True