Prevent lazy_property error on jobs registration

The _cache lazy_property fail on getattr, skip it. Under the hood,
inspect.getmembers() does exactly the same thing with dir and getattr.

queue_job/models/base.py

@@ -16,12 +16,20 @@ class Base(models.AbstractModel):
     def _register_hook(self):
         """ register marked jobs """
         super(Base, self)._register_hook()
-        job_methods = [method for __, method
-                       in inspect.getmembers(self, predicate=inspect.ismethod)
-                       if getattr(method, 'delayable', None)]
+        job_methods = set()
+        for attr_name in dir(self):
+            # _cache on models is a lazy_property which raises an
+            # AssertionError when called on a empty model, just skip it.
+            if attr_name == '_cache':
+                continue
+            try:
+                attr = getattr(self, attr_name)
+            except AttributeError:
+                continue
+            if inspect.ismethod(attr) and getattr(attr, 'delayable', None):
+                job_methods.add(attr)
         for job_method in job_methods:
             self.env['queue.job.function']._register_job(job_method)
-        # add_to_job_registry(job_methods)
 
     @api.multi
     def with_delay(self, priority=None, eta=None,