jar:file: stat fails with error 123 on Windows

it should be easy to reproduce reverting https://github.com/jruby/jruby/pull/6340/commits/c9b12c16487377d34ad02a98aaf3f4f7313b37a3 and running the test 
(`bin/jruby -S rake test:jruby TESTOPTS="--name=test_stat_directory_in_jar_with_trailing_slash"`)