Add: store headers for most savegame chunks

When a header is added, the chunk changes from CH_ARRAY type to
CH_TABLE type.

src/saveload/town_sl.cpp

@@ -325,9 +325,8 @@ static void Ptrs_TOWN()
 	}
 }
 
-/** Chunk handler for towns. */
 static const ChunkHandler town_chunk_handlers[] = {
-	{ 'HIDS', Save_HIDS, Load_HIDS, nullptr,   nullptr, CH_ARRAY },
+	{ 'HIDS', Save_HIDS, Load_HIDS, nullptr,   nullptr, CH_TABLE },
 	{ 'CITY', Save_TOWN, Load_TOWN, Ptrs_TOWN, nullptr, CH_ARRAY },
 };