[Bug] setup_git_env called without repository

[Zero King <l2dy@xxxxxxxxxxxx>]

Hi,

After upgrading to Git 2.13.0, I'm seeing the following error message
when running `git am -h`.

   $ git am -h
   fatal: BUG: setup_git_env called without repository

And with Git built from the next branch:

   $ git am -h
   BUG: environment.c:172: setup_git_env called without repository
   Abort trap: 6

--
Best regards,
Zero King