Fix scaling for empty lease.

[alrod]

CosmosDb trigger need at least one execution to initiate correct lease/checkpoint,

actually it works, we just missing a document in the beginning:

1. FunctionApp is deployed, no assigned workers.
2. SC handles "Non Found" - SC detect empty leases and add a new worker -> worker creates leases container and "ContinuationToken": null doc.
3. SC votes for 0 workers as Delta = 0.
4. Add a doc1 -> SC always votes for 1 worker as Delta = 1. We always have 1 assigned worker.
5. Add doc2 -> triggers executes on doc2 as we have an active worker - proper lease doc is created. The trigger executes fine from this point of time.
   doc1 has never triggered.

[ealsur]

Consider adding tests to cover the new behavior