Fix latent single-shard range hack

We had an off-by-one error when we fake #shard{} records for node local
databases. This fixes the issue. The bug was noticeable when attempting
to pass these shards to `fabric_view:is_progress_possible/1`.

BugzId: 22809
Merge pull request #58 from cloudant/22809-fix-fake-shard-range

Fix latent single-shard range hack