Guard Squirrel constructor_stub() invocations from invalid class parameters

This prevents manual invocations of the native class constructor for
non-class values or non-native classes.

Author: z33ky

sp/src/vscript/vscript_squirrel.cpp

@@ -1332,15 +1332,10 @@ SQInteger function_stub(HSQUIRRELVM vm)
 {
 	SQInteger top = sq_gettop(vm);
 
-	SQUserPointer userptr = nullptr;
-	if (SQ_FAILED(sq_getuserpointer(vm, top, &userptr)))
-	{
-		return sq_throwerror(vm, "Expected userpointer");
-	}
+	ScriptFunctionBinding_t* pFunc = nullptr;
+	sq_getuserpointer(vm, top, (SQUserPointer*)&pFunc);
 
-	Assert(userptr);
-
-	ScriptFunctionBinding_t* pFunc = (ScriptFunctionBinding_t*)userptr;
+	Assert(pFunc);
 
 	int nargs = pFunc->m_desc.m_Parameters.Count();
 	int nLastHScriptIdx = -1;
@@ -1548,7 +1543,15 @@ SQInteger destructor_stub_instance(SQUserPointer p, SQInteger size)
 SQInteger constructor_stub(HSQUIRRELVM vm)
 {
 	ScriptClassDesc_t* pClassDesc = nullptr;
-	sq_gettypetag(vm, 1, (SQUserPointer*)&pClassDesc);
+	if (SQ_FAILED(sq_gettypetag(vm, 1, (SQUserPointer*)&pClassDesc)))
+	{
+		return sq_throwerror(vm, "Expected native class");
+	}
+
+	if (!pClassDesc || (void*)pClassDesc == TYPETAG_VECTOR)
+	{
+		return sq_throwerror(vm, "Unable to obtain native class description");
+	}
 
 	if (!pClassDesc->m_pfnConstruct)
 	{