Example Chart.cs failing with th-th culture

[PBrunot]

It seems that LastIndexOf with Thai culture has a weird behaviour, maybe because it is a right to left language : the 0 position starts at the last character and then backwards to string beginning.
Since the indexes are "backwards", other code based on LastIndexOf() fail.

I observed it when the string begins with a dot with LastIndexOf(".").

To reproduce the issue run the LineChart.cs NPOI example with : CultureInfo.DefaultThreadCurrentCulture = new CultureInfo("th-th");

Exceptions happens in file extension strings manipulation code to generate the package during save.

[PBrunot]

To fix the exception in string manipulation, LastIndexOf must use StringComparison.Ordinal argument (see
https://www.jetbrains.com/help/resharper/StringLastIndexOfIsCultureSpecific.1.html )