Fixes #1567.

Looking for suggestions on how to add test coverage for this change. It seems like StackExchange.Redis.Tests.Streams.StreamGroupConsumerInfoGet() would be appropriate, but I'm not sure how to artificially increase the idle time of the consumer.

We could expose this layer to unit tests, but: that's something we can add later - I'm perfectly happy with the code as shown. Much appreciated fix, thanks.