t7005-editor: quote filename to fix whitespace-issue

t7005-editor: quote filename to fix whitespace-issue

Commit 4362da078e (t7005-editor: get rid of the SPACES_IN_FILENAMES
prereq, 2018-05-14) removed code for detecting whether spaces in
filenames work. Since we rely on spaces throughout the test suite
("trash directory.t1234-foo"), testing whether we can use the filename
"e space.sh" was redundant and unnecessary.

In simplifying the code, though, this introduced a regression around how
spaces are handled, not in the /name/ of the editor script, but /in/ the
script itself. The script just does `echo space >$1`, where $1 is for
example "/foo/t/trash directory.t7005-editor/.git/COMMIT_EDITMSG".

With most shells, or with Bash in posix mode, $1 will not be subjected
to field splitting. But if we invoke Bash directly, which will happen if
we build Git with SHELL_PATH=/bin/bash, it will detect and complain
about an "ambiguous redirect". More details can be found in [1], thanks
to SZEDER Gábor.

Make sure that the editor script quotes "$1" to remove the ambiguity.

[1] https://public-inbox.org/git/20180926121107.GH27036@localhost/

Signed-off-by: Alexander Pyhalov <apyhalov@gmail.com>
Commit-message-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>