Created by: deroko
Temporarily fixes issue on Windows 1903 where FLS data is not held in PEB anymore. This data is now spare data to keep PEB alignment.
Fix consists of avoiding app_peb->FlsBitmap when it doesn't exist. DynamoRIO will keep old FLS format in private_peb thus there is no problem when running on 1903.
Better solution would be to put FLS data in global variables inside of redir_ntdll.c thus there is no need to worry about if we are running on older windows or 1903, as anyhow private_peb FLS is initialized always from redir_ntdll.c so there would be no difference.