func (f *File) saveFileList(name string, content []byte) {
	newContent := make([]byte, 0, len(XMLHeader)+len(content))
	newContent = append(newContent, []byte(XMLHeader)...)
	newContent = append(newContent, content...)
	f.XLSX[name] = newContent
}
saveFileList provides function to update given file content in file list of
XLSX.
package excelize
import (
	"archive/zip"
	"bytes"
	"encoding/gob"
	"io"
	"log"
	"math"
	"unicode"
)
func ReadZipReader(r *zip.Reader) (map[string][]byte, int, error) {
	fileList := make(map[string][]byte)
	worksheets := 0
	for _, v := range r.File {
		fileList[v.Name] = readFile(v)
		if len(v.Name) > 18 {
			if v.Name[0:19] == "xl/worksheets/sheet" {
				worksheets++
			}
		}
	}
	return fileList, worksheets, nil
}
func (f *File) readXML(name string) []byte {
	if content, ok := f.XLSX[name]; ok {
		return content
	}
	return []byte{}
}