Codechange: mark chunks that are not stored as CH_READONLY

This makes it easier to spot chunks that have a save_proc that
is a nullptr, but also prevents confusion, where it looks like
the CH_ type of a chunk has influence on how it is being read.
It is not, it is only used for saving.

src/saveload/strings_sl.cpp

@@ -132,7 +132,7 @@ static void Load_NAME()
 
 /** Chunk handlers related to strings. */
 static const ChunkHandler name_chunk_handlers[] = {
-	{ 'NAME', nullptr, Load_NAME, nullptr, nullptr, CH_ARRAY },
+	{ 'NAME', nullptr, Load_NAME, nullptr, nullptr, CH_READONLY },
 };
 
 extern const ChunkHandlerTable _name_chunk_handlers(name_chunk_handlers);