grep: fix "--quiet" overwriting current output
grep: fix "--quiet" overwriting current output

When grep is called with the --quiet option, the pager is initialized
despite not being used.  When the pager is "less", anything output by
previous commands and not ended with a newline is overwritten:

    $ echo -n aaa; echo bbb
    aaabbb
    $ echo -n aaa; git grep -q foo; echo bbb
    bbb

This can be worked around, for example, by making sure STDOUT is not a
TTY or more directly by setting git's pager to "cat":

    $ echo -n aaa; git grep -q foo > /dev/null; echo bbb
    aaabbb
    $ echo -n aaa; PAGER=cat git grep -q foo; echo bbb
    aaabbb

But prevent calling the pager in the first place, which would also
save an unnecessary fork().

Signed-off-by: Wilhelm Schuermann <36c6c9424bb1b393a6b908a8a6816ca93d3f0a0c@googlemail.com>
Reviewed-by: Jeff King <696e3fbcf235d40b6ea1ebd61c87cbea79d444e7@peff.net>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git