LazUtils: fix LazFileUtils.FileIsText when filename has unicode characters outside currrent codepage on Windows.
Needs refactoring of LazUtf8Classes (use LazFileUtils instead of FileUtil).
Next step in moving UTF89 file routines to LazFileUil.


git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@41209 4005530d-fff6-0310-9dd1-cebe43e6787f