Creating a sheet without calling write_sheet afterwards causing excel detection of corrupted file

[gwy15]

If a sheet is created without writing any data to it using the write_sheet method afterwards, excel warns that the file is corrupted and asks whether excel should try to fix it. Normally this can be auto-fixed.

A call to write_sheet without any data actually written will eliminate this excel warning.

example code

let mut wb = Workbook::create("/tmp/b.xlsx");
let mut _sheet = wb.create_sheet("SheetName");
wb.close().expect("close excel error!");