dir: respect string length argument of read_directory_recursive()

A directory name is passed to read_directory_recursive() as a
length-limited string, through the parameters base and baselen.
Suprisingly, base must be a NUL-terminated string as well, as it is
passed to opendir(), ignoring baselen.

Fix this by postponing the call to opendir() until the length-limted
string is added to a strbuf, which provides a NUL in the right place.

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

dir.c

@@ -960,16 +960,17 @@ static int read_directory_recursive(struct dir_struct *dir,
 				    int check_only,
 				    const struct path_simplify *simplify)
 {
-	DIR *fdir = opendir(*base ? base : ".");
+	DIR *fdir;
 	int contents = 0;
 	struct dirent *de;
 	struct strbuf path = STRBUF_INIT;
 
-	if (!fdir)
-		return 0;
-
 	strbuf_add(&path, base, baselen);
 
+	fdir = opendir(path.len ? path.buf : ".");
+	if (!fdir)
+		goto out;
+
 	while ((de = readdir(fdir)) != NULL) {
 		switch (treat_path(dir, de, &path, baselen, simplify)) {
 		case path_recurse:
@@ -984,12 +985,11 @@ static int read_directory_recursive(struct dir_struct *dir,
 		}
 		contents++;
 		if (check_only)
-			goto exit_early;
+			break;
-		else
 		dir_add_name(dir, path.buf, path.len);
 	}
-exit_early:
 	closedir(fdir);
+ out:
 	strbuf_release(&path);
 
 	return contents;