server selection: don't skip server state check when dealing with one server
server selection: don't skip server state check when dealing with one server

omcache_command() used to skip calling ketama for server selection when we
only used a single server.  this unfortunately meant that we skipped the
whole server state validation that's done by the ketama lookup function.

thedrow/omcache,ohmu/omcache,CrowdStrike/omcache,CrowdStrike/omcache,thedrow/omcache,ohmu/omcache