OperatorPublish connect(connection) should not return null

[davidmoten]

This is outstanding work from #2774. I can have a go at it next week if no-one in a rush.

[akarnokd]

If you don't mind some Reactive-Streams style code, you can look at my OperatorPublish which definitely doesn't return null on connec, but due to the half-finished project, I can't run all tests relying on it.

[davidmoten]

Looks to me that OperatorPublish needs a good chunk of rework (#2810) and that the ReactiveStreams code could be basis for a rewrite. I'd be happy to have a go at this but haven't much time on my hands this week and anyway it might make more sense for @akarnokd to do it as he's so familiar with the subject already (and would probably do it in the blink of an eye).

[akarnokd]

I'll add this to my todo list for this week.

[akarnokd]

The operator has been rewritten so it never returns null. Closing.