fix the untagged server selection

Author: Ithanil

app/models/server.rb

@@ -308,13 +308,13 @@ def self.find_available(tags_arg = nil)
           ids_loads_tagged.concat ids_loads.select { |myid, _| redis.hget(key(myid), 'tag') == tag }
         end
         ids_loads_tagged.sort_by { |id_load| id_load[1] }
-        if ids_loads_tagged.blank?
-          raise BBBErrors::ServerTagUnavailableError, tags_arg if tags_required
-          tags = nil # fall back to servers without tag
-          ids_loads_tagged = ids_loads.select { |myid, _| redis.hget(key(myid), 'tag').nil? }
-        end
-        ids_loads = ids_loads_tagged
       end
+      if ids_loads_tagged.blank?
+        raise BBBErrors::ServerTagUnavailableError, tags_arg if tags_required
+        tags = nil # fall back to servers without tag
+        ids_loads_tagged = ids_loads.select { |myid, _| redis.hget(key(myid), 'tag').nil? }
+      end
+      ids_loads = ids_loads_tagged
 
       # try to select the server with lowest load
       id, load, hash = ids_loads.each do |id, load|