- fixed crash on message output during decorate parsing

Script position is now initialized at the very beginning of decorate parsing process
Script position no longer contains uninitialized file name

https://forum.zdoom.org/viewtopic.php?t=64836

src/sc_man.cpp

@@ -1174,6 +1174,13 @@ FScriptPosition &FScriptPosition::operator=(const FScriptPosition &other)
 	return *this;
 }
 
+FScriptPosition &FScriptPosition::operator=(FScanner &sc)
+{
+	FileName = sc.ScriptName;
+	ScriptLine = sc.GetMessageLine();
+	return *this;
+}
+
 //==========================================================================
 //
 // FScriptPosition::Message

src/sc_man.h

@@ -167,12 +167,14 @@ struct FScriptPosition
 
 	FScriptPosition()
 	{
+		FileName = NAME_None;
 		ScriptLine=0;
 	}
 	FScriptPosition(const FScriptPosition &other);
 	FScriptPosition(FString fname, int line);
 	FScriptPosition(FScanner &sc);
 	FScriptPosition &operator=(const FScriptPosition &other);
+	FScriptPosition &operator=(FScanner &sc);
 	void Message(int severity, const char *message,...) const GCCPRINTF(3,4);
 	static void ResetErrorCounter()
 	{

src/scripting/decorate/thingdef_parse.cpp

@@ -1151,6 +1151,7 @@ static void ParseActor(FScanner &sc, PNamespace *ns)
 	bag.Namespace = ns;
 	bag.Version = { 2, 0, 0 };	
 	bag.fromDecorate = true;
+	bag.ScriptPosition = sc;
 	info = ParseActorHeader(sc, &bag);
 	sc.MustGetToken('{');
 	while (sc.MustGetAnyToken(), sc.TokenType != '}')