Bug: git-gui stops showing untracked files when invalid .git file is present in a subfolder

To reproduce:

git init testrepo
cd testrepo
touch test.txt
mkdir sub
echo 'gitdir: path/to/nowhere' >> sub/.git
git gui


Displays no files/changes, no error message.
Should display test.txt in git-gui. Or possibly fail with error
(though git status does not fail).
Shell should display error message.


Observed on Ubuntu 13.10 using
git version 1.8.3.2
git-gui version 0.17.0

Note the same happens when writing rubbish like 'xyz' into that .git
file (Violating gitfile format).

Note that when trying to launch git gui from that subfolder, I get a
valid error message:
fatal: Not a git repository: path/to/nowhere
same as when running git status

I guess that git-gui tries to do something with submodules, but some
failure is not handled well.

regards,
  Thibault