t7502: properly quote GIT_EDITOR

t7502: properly quote GIT_EDITOR

One of the tests tries to ensure that editor is not run due
to an early failure. However, it needs to quote the pathname
of the trash directory used in $GIT_EDITOR, since git will
pass it along to the shell. In other words, the test would
pass whether the code was correct or not, since the unquoted
editor specification would never run.

We never noticed the problem because the code is indeed
correct, so git-commit never even tried to run the editor.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>