FastExcel incorrectly handles decimal separator (eg Russian ,)

[ryan-de-boer]

When running under a Russian environment with ',' separator, FastExcel creates xlsx files that Excel reports as corrupt and it repairs them. This is caused by FastExcel using the implicit ToString() on double and decimal Value types in Cell.ToXmlString. This writes for example '1,2' to the xml string. Excel only supports an xml string with dot as the decimal separator, eg '1.2'. By forcing the decimal separator to '.' in the current thread prior to using fastExcel.Write, it solves the issue but it is an undesirable workaround. It would be better if FastExcel wrote '.' as the decimal separator without globally changing the separator. The dot is only in the file format, Excel correctly displays ',' in the UI.

Here is how I fixed it:
fix.txt
I uploaded it as txt, since the whitespace was removed from the code fragments from this post making it hard to read.