Round-robin queue resets now leave the Redis queue empty when an inbox
has no members, avoiding an invalid sorted-set write while keeping
normal queue population unchanged.
## Closes
-
[CW-7922](https://linear.app/chatwoot/issue/CW-7922/harden-backend-paths-causing-production-sentry-errors)
- [Sentry 7663380084](https://chatwoot-p3.sentry.io/issues/7663380084/)
## How to reproduce
Run round-robin assignment for an inbox with no inbox members. Resetting
the queue previously attempted a Redis sorted-set write without any
member/score pairs.
## What changed
- Clear the existing queue as before.
- Skip queue population when there are no eligible user IDs.
- Add service coverage for an inbox with no members.
8a778f4f5b