Fixed set_unique_id script function

* it unassigned unique ID even when the object doesn't have one.
* it didn't sync the attached script's owner id after unassignment.

Added a safeguard to prevent item_identical function returning false
when comparing a unique_id item to itself.

(ref. fallout2-ce/fallout2-ce#466)

sfall/Modules/Objects.cpp

@@ -35,7 +35,7 @@ bool Objects::IsUniqueID(long id) {
 	return (id > UniqueID::Start || (id >= fo::PLAYER_ID && id < 83536)); // 65535 maximum possible number of prototypes
 }
 
-static void SetScriptObjectID(fo::GameObject* obj) {
+void Objects::SetScriptObjectID(fo::GameObject* obj) {
 	fo::ScriptInstance* script;
 	if (fo::func::scr_ptr(obj->scriptId, &script) != -1) {
 		script->ownerObjectId = obj->id;
@@ -74,8 +74,11 @@ void Objects::SetNewEngineID(fo::GameObject* obj) {
 }
 
 static __declspec(naked) void item_identical_hack() {
+	static const DWORD item_identical_End = 0x477AD5;
 	using namespace fo::Fields;
 	__asm {
+		cmp  esi, edi;   // inv_item == place_item? (safeguard)
+		je   identical;
 		mov  ecx, [edi]; // place_item id
 		cmp  ecx, Start; // start unique ID
 		jg   notIdentical;
@@ -87,6 +90,9 @@ static __declspec(naked) void item_identical_hack() {
 		cmp  eax, ebx;
 notIdentical:
 		retn; // if ZF == 0 then item is not identical
+identical:
+		add  esp, 4;
+		jmp  item_identical_End;
 	}
 }
 
@@ -111,7 +117,7 @@ static void map_fix_critter_id() {
 		if (obj->IsCritter()) {
 			if (obj->id < fo::PLAYER_ID) {
 				obj->id = npcStartID++;
-				SetScriptObjectID(obj);
+				Objects::SetScriptObjectID(obj);
 			}
 			Stats::UpdateHPStat(obj);
 		}

sfall/Modules/Objects.h

@@ -36,6 +36,7 @@ public:
 	static long uniqueID;
 
 	static bool IsUniqueID(long id);
+	static void SetScriptObjectID(fo::GameObject* obj);
 
 	static long __fastcall SetObjectUniqueID(fo::GameObject* obj);
 	static long __fastcall SetSpecialID(fo::GameObject* obj);

sfall/Modules/Scripting/Handlers/Objects.cpp

@@ -584,14 +584,16 @@ void mf_set_drugs_data(OpcodeContext& ctx) {
 
 void mf_set_unique_id(OpcodeContext& ctx) {
 	fo::GameObject* obj = ctx.arg(0).object();
-	long id;
-	if (ctx.arg(1).rawValue() == -1) {
-		id = fo::func::new_obj_id();
-		obj->id = id;
-	} else {
-		id = Objects::SetObjectUniqueID(obj);
+	if (ctx.numArgs() > 1 && ctx.arg(1).rawValue() == -1) {
+		// unassign unique ID only if the object currently has one
+		if (obj->id > UniqueID::Start) {
+			obj->id = fo::func::new_obj_id();
+			Objects::SetScriptObjectID(obj);
+		}
+		ctx.setReturn(obj->id);
+		return;
 	}
-	ctx.setReturn(id);
+	ctx.setReturn(Objects::SetObjectUniqueID(obj));
 }
 
 void mf_objects_in_radius(OpcodeContext& ctx) {