SD:Consul - Index handling is incorrect per consul docs

[schmidtw]

The loop where index handling is incorrect.

Consul Docs
https://www.consul.io/api-docs/features/blocking#implementation-details

Index goes backwards

In rare cases, the index can be returned that is before the last index. In this case, the system can basically miss out on events for either a very long time or forever. This can be pretty damaging if you depend on the consistency of the SD value & the value does not appropriately update.

Index returned is zero

In rare cases the returned index can be zero. In this case the code should backoff and try again to avoid a tight loop.

[schmidtw]

I have a proposed fix for these two errors in my local repo.
https://github.com/schmidtw/kit/commit/e539a98781cb06b55e5f787254627b720f21e8ff

[peterbourgon]

Happy to take a PR.

[sagikazarmark]

Fixed in #999