fix: avoid timeout if datacenter does not exist in topology (#5772)

* fix: avoid timeout if datacenter does not exist in topology

* fix: error msg

* fix: rm dublicate check

* fix: compare

* revert minor change

weed/server/master_server_handlers.go

@@ -126,6 +126,13 @@ func (ms *MasterServer) dirAssignHandler(w http.ResponseWriter, r *http.Request)
 		startTime  = time.Now()
 	)
 
+	if !ms.Topo.DataCenterExists(option.DataCenter) {
+		writeJsonQuiet(w, r, http.StatusBadRequest, operation.AssignResult{
+			Error: fmt.Sprintf("data center %v not found in topology", option.DataCenter),
+		})
+		return
+	}
+
 	for time.Now().Sub(startTime) < maxTimeout {
 		fid, count, dnList, shouldGrow, err := ms.Topo.PickForWrite(requestedCount, option, vl)
 		if shouldGrow && !vl.HasGrowRequest() {