Prevent players from declaring ready after round start

Adds a check when declaring ready (or canceling it) to prevent Ready
from being anything other than 0 after round has started.

This prevents display bugs from allowing a player to accidentally lock
their setup after the round has started.
Adds a final fallback join location

In the event that a rank has no spawn location, this change will cause
them to spawn at a JoinLate landmark instead.