win32u: Correct the packed size of WM_GETDLGCODE when lparam is NULL.

dlls/win32u/message.c

@@ -1691,7 +1691,7 @@ size_t user_message_size( HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam,
         size = sizeof(STYLESTRUCT);
         break;
     case WM_GETDLGCODE:
-        size = sizeof(MSG);
+        if (lparam) size = sizeof(MSG);
         break;
     case SBM_SETSCROLLINFO:
     case SBM_GETSCROLLINFO:

dlls/win32u/tests/win32u.c

@@ -1063,7 +1063,6 @@ static void test_inter_process_child( HWND hwnd )
     ok( res == 4, "res = %d\n", res );
 
     res = NtUserMessageCall( hwnd, WM_GETDLGCODE, 0, 0, NULL, NtUserSendMessage, TRUE );
-    todo_wine
     ok( res == 1, "res = %d\n", res );
 
     mdi.szClass = "TestClass";