Greg Price 4b5c52fc99 queue: Prevent an AttributeError rather than swallowing it. ...

When the RabbitMQ server disappears, we log errors like these:

```
Traceback (most recent call last):
  File "./zerver/lib/queue.py", line 114, in json_publish
    self.publish(queue_name, ujson.dumps(body))
  File "./zerver/lib/queue.py", line 108, in publish
    self.ensure_queue(queue_name, do_publish)
  File "./zerver/lib/queue.py", line 88, in ensure_queue
    if not self.connection.is_open:
AttributeError: 'NoneType' object has no attribute 'is_open'

During handling of the above exception, another exception occurred:
[... traceback of connection failure inside the retried self.publish()]
```

That's a type error -- a programming error, not an exceptional
condition from outside the program.  Fix the programming error.

Also move the retry out of the `except:` block, so that if it also
fails we don't get the exceptions stacked on each other.  This is a
new feature of Python 3 which is sometimes indispensable for
debugging, and which surfaced this nit in the logs (on Python 2 we'd
never see the AttributeError part), but in some cases it can cause a
lot of spew if care isn't taken.

2017-11-16 18:33:14 -08:00

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