[PATCH 1/4] worktree add: don't read out of bounds in worktree_basename()

["René Scharfe" <l.s.r@web.de>]

When we search for the start of the basename and `len` is zero, `name`
ends up being `path` - 1, out of bounds.  Avoid that by checking before
decrementing.

Fixes https://github.com/git-for-windows/git/issues/6346.

Original-patch-by: Matthias Aßhauer <mha1993@live.de>
Signed-off-by: René Scharfe <l.s.r@web.de>
---
 builtin/worktree.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/builtin/worktree.c b/builtin/worktree.c
index 654d27c3e1..a770dd5ead 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -303,11 +303,9 @@ static const char *worktree_basename(const char *path, int *olen)
 	while (len && is_dir_sep(path[len - 1]))
 		len--;
 
-	for (name = path + len - 1; name > path; name--)
-		if (is_dir_sep(*name)) {
-			name++;
-			break;
-		}
+	name = path + len;
+	while (name > path && !is_dir_sep(name[-1]))
+		name--;
 
 	*olen = len;
 	return name;
-- 
2.55.0