Issue #15478: Raising an OSError doesn't decode or encode the filename anymore

Issue #15478: Raising an OSError doesn't decode or encode the filename anymore

Pass the original filename argument to OSError constructor, instead of trying
to encode it to or decode it from the filesystem encoding. This change avoids
an additionnal UnicodeDecodeError on Windows if the filename cannot be decoded
from the filesystem encoding (ANSI code page).