t5528: do not fail with FreeBSD shell

The FreeBSD shell converts this expression:

  git ${1:+-c push.default="$1"} push

to this when "$1" is not empty:

  git "-c push.default=$1" push

which causes git to fail.  To avoid this we simply break up the
expansion into two parts so that the whitespace which creates
two arguments instead of one is outside the ${...} like so:

  git ${1:+-c} ${1:+push.default="$1"} push

This has the desired effect on all platforms allowing the test
to pass on FreeBSD.
Signed-off-by: NKyle J. McKay <mackyle@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

t/t5528-push-default.sh

@@ -26,7 +26,7 @@ check_pushed_commit () {
 # $2 = expected target branch for the push
 # $3 = [optional] repo to check for actual output (repo1 by default)
 test_push_success () {
-	git ${1:+-c push.default="$1"} push &&
+	git ${1:+-c} ${1:+push.default="$1"} push &&
 	check_pushed_commit HEAD "$2" "$3"
 }
 
@@ -34,7 +34,7 @@ test_push_success () {
 # check that push fails and does not modify any remote branch
 test_push_failure () {
 	git --git-dir=repo1 log --no-walk --format='%h %s' --all >expect &&
-	test_must_fail git ${1:+-c push.default="$1"} push &&
+	test_must_fail git ${1:+-c} ${1:+push.default="$1"} push &&
 	git --git-dir=repo1 log --no-walk --format='%h %s' --all >actual &&
 	test_cmp expect actual
 }