Fix LanguageContainer Constructor order + Retrieving LanguageFileName exception on empty culture (Ubuntu)

[RickVanSnippenburg]

Some fixes for minor issues I ran into while attempting to run my Blazor web project using the Multilanguage library in Ubuntu (WSL/Docker):

• Fix the order of the LanguageContainer constructors (the base Constructor gets called before the derived one does).
• On Ubuntu (WSL/Docker) the CultureInfo.CurrentCulture seems to be empty by default, resulting in an exception in the GetKeys method of the GetKeysProvider. The SingleOrDefault on line 32 threw an exception, because the SingleOrDefault expression resulted in retrieving all the yml language files.

[aksoftware98]

Thank you so much for this, much appreciated the new version will be released in an hour or so.