admin: only claim fallback master leadership on an empty raft response

A nonempty RaftListClusterServers response whose entries were all
rejected left masterMap empty, so the fallback marked the reachable
current master as leader the same way a genuinely empty (non-raft)
response does. Track whether the successful response returned zero
servers and only promote the fallback master then.

weed/admin/dash/admin_data.go

@@ -282,7 +282,7 @@ func (s *AdminServer) ShowOverview(w http.ResponseWriter, r *http.Request) {
 // dashboard never shows an empty list.
 func (s *AdminServer) getMasterNodesStatus() []MasterNode {
 	masterMap := make(map[string]MasterNode)
-	raftCallSucceeded := false
+	raftReturnedEmpty := false
 
 	err := s.WithMasterClient(func(client master_pb.SeaweedClient) error {
 		ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
@@ -291,7 +291,7 @@ func (s *AdminServer) getMasterNodesStatus() []MasterNode {
 		if err != nil {
 			return err
 		}
-		raftCallSucceeded = true
+		raftReturnedEmpty = len(resp.ClusterServers) == 0
 		for _, server := range resp.ClusterServers {
 			// Skip malformed raft addresses instead of letting an
 			// unconvertible value into masterMap.
@@ -323,10 +323,11 @@ func (s *AdminServer) getMasterNodesStatus() []MasterNode {
 			addr := pb.ServerAddress(currentMaster).ToHttpAddress()
 			// A successful empty raft response means raft is not initialized
 			// (standalone/non-raft cluster); the only master IS the leader.
-			// A failed RPC means connectivity issue; do not claim leadership.
+			// A failed RPC or a nonempty response whose entries were all
+			// rejected must not claim leadership.
 			masterMap[addr] = MasterNode{
 				Address:  addr,
-				IsLeader: raftCallSucceeded,
+				IsLeader: raftReturnedEmpty,
 			}
 		}
 	}

weed/admin/dash/admin_server.go

@@ -1341,11 +1341,13 @@ func (s *AdminServer) GetClusterMasters() (*ClusterMastersData, error) {
 	}
 
 	// Then, get additional master information from Raft cluster
+	raftReturnedEmpty := false
 	err = s.WithMasterClient(func(client master_pb.SeaweedClient) error {
 		resp, err := client.RaftListClusterServers(context.Background(), &master_pb.RaftListClusterServersRequest{})
 		if err != nil {
 			return err
 		}
+		raftReturnedEmpty = len(resp.ClusterServers) == 0
 
 		// Process each raft server
 		for _, server := range resp.ClusterServers {
@@ -1401,10 +1403,12 @@ func (s *AdminServer) GetClusterMasters() (*ClusterMastersData, error) {
 		if currentMaster != "" {
 			masters = append(masters, MasterInfo{
 				Address:  pb.ServerAddress(currentMaster).ToHttpAddress(),
-				IsLeader: true,
+				IsLeader: raftReturnedEmpty,
 				Suffrage: "Voter",
 			})
-			leaderCount = 1
+			if raftReturnedEmpty {
+				leaderCount = 1
+			}
 		}
 	}