fix nil raft server caused crash

fix https://github.com/chrislusf/seaweedfs/issues/524

weed/server/master_server_handlers_ui.go

@@ -3,26 +3,25 @@ package weed_server
 import (
 	"net/http"
 
+	"github.com/chrislusf/raft"
+	ui "github.com/chrislusf/seaweedfs/weed/server/master_ui"
 	"github.com/chrislusf/seaweedfs/weed/stats"
 	"github.com/chrislusf/seaweedfs/weed/util"
-	ui "github.com/chrislusf/seaweedfs/weed/server/master_ui"
 )
 
 func (ms *MasterServer) uiStatusHandler(w http.ResponseWriter, r *http.Request) {
 	infos := make(map[string]interface{})
 	infos["Version"] = util.VERSION
 	args := struct {
-		Version  string
-		Topology interface{}
-		Leader   string
-		Peers    interface{}
-		Stats    map[string]interface{}
-		Counters *stats.ServerStats
+		Version    string
+		Topology   interface{}
+		RaftServer raft.Server
+		Stats      map[string]interface{}
+		Counters   *stats.ServerStats
 	}{
 		util.VERSION,
 		ms.Topo.ToMap(),
-		ms.Topo.RaftServer.Leader(),
-		ms.Topo.RaftServer.Peers(),
+		ms.Topo.RaftServer,
 		infos,
 		serverStats,
 	}