win32/file.c: fix target encoding

* win32/file.c (fix_string_encoding): fix target encoding.  the
  parameter `encoding' is not the target encoding but the original
  encoding.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42190 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
win32/file.c: suppress warning

* win32/file.c (convert_mb_to_wchar): omit never-true NULL check to
  suppress maybe-uninitialized warning in rb_file_load_ok().

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42191 b2dd03c8-39d4-4d8f-98ff-823fe69b080e