SimpleStrategy creates a list of endpoints by iterating over the set of
all configured endpoints for the given token, until we reach keyspace
replication factor.
There is a trivial coding bug when we first add at least one endpoint
to the list, and then compare list size and replication factor.
If RF=0 this never yields true.
Fix by moving the RF check before at least one endpoint is added to the
list.
Cassandra never had this bug since it uses a less fancy while()
loop.
Fixes#5962
Message-Id: <20200306193729.130266-1-kostja@scylladb.com>