Avoid out of bounds exception if checksum is ok but data is crap

main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"bytes"
 	"flag"
+	"fmt"
 	"io"
 	"log"
 	"os"
@@ -155,6 +156,11 @@ func treatLine(line []byte, legacyMode bool) (key string, horodate *time.Time, d
 
 	fields := bytes.Fields(line)
 
+	if len(fields) < 2 {
+		err = fmt.Errorf("Invalid number of fields in line")
+		return
+	}
+
 	key = string(fields[0])
 
 	horodate, err = getHorodate(&fields)