Bug: `gitsubmodule` does not list modules with unicode characters

The `git submodule` commands seem to ignore modules which paths contain
unicode characters.

Consider the following steps to reproduce the problem:

  1. Create a directory with name that contains at least one unicode character
     (e.g. "ûñïçödé-rèpø")

  2. Initialize git repository within this directory

  3. Add this repository as a submodule to another repository so that
     unicode characters will appear in the path to the module
     (e.g. "../ûñïçödé-rèpø")

  4. Check that .gitmodules file is updated and contains record
     about just added module

  5. List submodules with using `git submodule` and find out
     that just added module is not listed