Allow place_param2 = 0 node placement predictions (#13787)

The placement prediction value 0 was accidentally ignored
and made the clients fall back to automatic rotation based
on the node paramtype2 value.

This now changes the internal representation to properly
indicate the disabled state (e.g. 'nil' in Lua).

src/itemdef.h

@@ -23,6 +23,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "irrlichttypes_extrabloated.h"
 #include <string>
 #include <iostream>
+#include <optional>
 #include <set>
 #include "itemgroup.h"
 #include "sound.h"
@@ -87,7 +88,7 @@ struct ItemDefinition
 	// Server will update the precise end result a moment later.
 	// "" = no prediction
 	std::string node_placement_prediction;
-	u8 place_param2;
+	std::optional<u8> place_param2;
 
 	/*
 		Some helpful methods