Commit 55f0566 (get_local_heads(): do not return random pointer if
there is no head, 2009-04-17) fixed a segfault for git push, this
patch adds a test-case to avoid future regressions.
Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr> Signed-off-by: Junio C Hamano <gitster@pobox.com>