libselinux: label_db::db_init(): open file with CLOEXEC mode

Open the file stream with the `e` flag, so that the underlying file
descriptor gets closed on an exec in a potential sibling thread.

Also drop the flag `b`, since it is ignored on POSIX systems.

Found by clang-tidy.

Signed-off-by: Christian Göttsche <cgzones@googlemail.com>

libselinux/src/label_db.c

@@ -277,7 +277,7 @@ db_init(const struct selinux_opt *opts, unsigned nopts,
 	if (!path)
 		path = selinux_sepgsql_context_path();
 
-	if ((filp = fopen(path, "rb")) == NULL) {
+	if ((filp = fopen(path, "re")) == NULL) {
 		free(catalog);
 		return NULL;
 	}