fix crash when most active IP list cannot be saturated

(This could have been cleaner by first using Min() or something)

fixes #550

server/startup.go

@@ -166,6 +166,9 @@ func Serve(ctx *cli.Context) error {
 				builder := strings.Builder{}
 				var item kv
 				for i := uint(0); i < cfg.Server.MostActiveIpCount; i++ {
+					if i >= uint(len(kvArray)) {
+						break
+					}
 					item = kvArray[i]
 					builder.WriteString(fmt.Sprintf("\n%s, %d", item.Key, item.Value))
 				}