wow64win: Skip WM_CREATE/WM_NCCREATE lParam conversion if NULL.

lParam being NULL is handled in win32u/defwnd.c so make sure to pass the NULL
through rather than relying on the pointer always being valid since it may not
be in this case.

dlls/wow64win/user.c

@@ -3264,6 +3264,7 @@ static LRESULT message_call_32to64( HWND hwnd, UINT msg, WPARAM wparam, LPARAM l
     {
     case WM_NCCREATE:
     case WM_CREATE:
+        if (lparam)
         {
             CREATESTRUCT32 *cs32 = (void *)lparam;
             CREATESTRUCTW cs;
@@ -3282,6 +3283,7 @@ static LRESULT message_call_32to64( HWND hwnd, UINT msg, WPARAM wparam, LPARAM l
             cs32->dwExStyle      = cs.dwExStyle;
             return ret;
         }
+        return NtUserMessageCall( hwnd, msg, wparam, lparam, result_info, type, ansi );
 
     case WM_MDICREATE:
         {