Return empty list instead of InconsistencyError when exchange table is empty

[matusvalo]

Missing redis key containg set of queues bound to queue is caused
by removal all queues from the exchange. Hence, we should not raise an
exception but just return empty list of queues instead. This commit
fixes e.g. case publishing message against empty exchange:

import kombu
conn = kombu.Connection('redis://')
exchange = kombu.Exchange('name', type='direct')
exchange.declare(channel=conn.default_channel)

producer = conn.Producer()
producer.publish(
     {'hello': 'world'},
     exchange=exchange,
     routing_key='queue1'
)

But it also fixes the case when last queue is unbound from exchange and
after publishing to this exchange:

import kombu
conn = kombu.Connection('redis://')
exchange = kombu.Exchange('name', type='direct')
queue1 = kombu.Queue('queue1', exchange=exchange, routing_key='queue1')
exchange.declare(channel=conn.default_channel)
queue1 = queue1.bind(channel=conn.default_channel)
queue1.declare()

producer = conn.Producer()
producer.publish(
     {'hello': 'world'},
     exchange=exchange,
     routing_key='queue1'
)

queue1.delete()

producer.publish(
     {'hello': 'world'},
     exchange=exchange,
     routing_key='queue1'
)

Fixes #1063

[auvipy]

the fix look good to me but the non pypy integration test failed for some reason.

[matusvalo]

the fix look good to me but the non pypy integration test failed for some reason.

The pypy integration test is failing a long time. Not sure why.

[auvipy]

yeah but im talking about other integrations tests. the tools that run CI needs some minor tweaks. like pypy should be pypy-3.7 etc. I have to check docs and try to fix them this week

[matusvalo]

yeah but im talking about other integrations tests.

The other int. tests were canceled since the one failed. The failing one ideally should be fixed but I dont have time for that right now.

[auvipy]

yeah the CI can use pypy more then 3.6 thats the issue