[PATCH 2/2] check-ignore.c: fix segfault with '.' argument from repo root

[Adam Spiers <git@adamspiers.org>]

Fix a corner case where check-ignore would segfault when run with the
'.' argument from the top level of a repository, due to prefix_path()
converting '.' into the empty string.  It doesn't make much sense to
call check-ignore from the top level with '.' as a parameter, since
the top-level directory would never typically be ignored, but of
course it should not segfault in this case.

Signed-off-by: Adam Spiers <git@adamspiers.org>
---
 builtin/check-ignore.c | 2 +-
 t/t0008-ignores.sh     | 5 +++++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/builtin/check-ignore.c b/builtin/check-ignore.c
index 709535c..b0dd7c2 100644
--- a/builtin/check-ignore.c
+++ b/builtin/check-ignore.c
@@ -89,7 +89,7 @@ static int check_ignore(const char *prefix, const char **pathspec)
 					? strlen(prefix) : 0, path);
 		full_path = check_path_for_gitlink(full_path);
 		die_if_path_beyond_symlink(full_path, prefix);
-		if (!seen[i] && path[0]) {
+		if (!seen[i] && full_path[0]) {
 			exclude = last_exclude_matching_path(&check, full_path,
 							     -1, &dtype);
 			if (exclude) {
diff --git a/t/t0008-ignores.sh b/t/t0008-ignores.sh
index ebe7c70..9c1bde1 100755
--- a/t/t0008-ignores.sh
+++ b/t/t0008-ignores.sh
@@ -138,6 +138,7 @@ test_expect_success 'setup' '
 	cat <<-\EOF >.gitignore &&
 		one
 		ignored-*
+		top-level-dir/
 	EOF
 	for dir in . a
 	do
@@ -177,6 +178,10 @@ test_expect_success 'setup' '
 #
 # test invalid inputs
 
+test_expect_success_multi '. corner-case' '' '
+	test_check_ignore . 1
+'
+
 test_expect_success_multi 'empty command line' '' '
 	test_check_ignore "" 128 &&
 	stderr_contains "fatal: no path specified"
-- 
1.8.1.291.g0730ed6