light-4j 1.6.x : Add check for Consul Index < 1

[mihai-vladuc]

Sanity check index is greater than zero. After the initial request (or a reset as above) the X-Consul-Index returned should always be greater than zero. It is a bug in Consul if it is not, however this has happened a few times and can still be triggered on some older Consul versions. It's especially bad because it causes blocking clients that are not aware to enter a busy loop, using excessive client CPU and causing high load on servers. It is always safe to use an index of 1 to wait for updates when the data being requested doesn't exist yet, so clients should sanity check that their index is at least 1 after each blocking response is handled to be sure they actually block on the next request.

https://developer.hashicorp.com/consul/api-docs/features/blocking