when CWD is uri:classloader:/ regular absolute path do not work

```
$ bin/jruby -e "f = File.expand_path('pom.xml');Dir.chdir('uri:classloader:/');p File.new(f)"
Errno::ENOENT: No such file or directory - uri:classloader:/home/christian/jruby/pom.xml
  initialize at org/jruby/RubyFile.java:363
         new at org/jruby/RubyIO.java:853
      (root) at -e:1
```
