Introduced in 9ebdeb2
The problem is specific to node replacing and rack-list RF. The
culprit is in the part of the load balancer which determines rack's
shard count. If we're replacing the last node, the rack will contain
no normal nodes, and shards_per_rack will have no entry for the rack,
on which the table still has replicas. This throws std::out_of_range
and fails the tablet draining stage, and node replace is failed.
No backport because the problem exists only on master.
Fixes#26768Closesscylladb/scylladb#26783
f8879d797d