db/update/Archive: validate directory names

Fixes assertion failure if the ZIP file contains a path that begins
with a slash.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1793

NEWS

@@ -14,6 +14,7 @@ ver 0.24 (not yet released)
   - proxy: require libmpdclient 2.15 or later
 * archive
   - add option to disable archive plugins in mpd.conf
+  - zzip: fix crash bug
 * input
   - curl: add "connect_timeout" configuration
   - curl: fix busy loop after connection failed

src/db/update/Archive.cxx

@@ -50,6 +50,9 @@ UpdateWalk::UpdateArchiveTree(ArchiveFile &archive, Directory &directory,
 {
 	const auto [child_name, rest] = Split(name, '/');
 	if (rest.data() != nullptr) {
+		if (!IsAcceptableFilename(child_name))
+			return;
+
 		//add dir is not there already
 		Directory *subdir = LockMakeChild(directory, child_name);
 		subdir->device = DEVICE_INARCHIVE;