comctl32/datetime: Don't check box if no valid date set.

dlls/comctl32/datetime.c

@@ -1402,7 +1402,7 @@ DATETIME_StyleChanged(DATETIME_INFO *infoPtr, WPARAM wStyleType, const STYLESTRU
         infoPtr->hwndCheckbut = CreateWindowExW (0, WC_BUTTONW, 0, WS_CHILD | WS_VISIBLE | BS_AUTOCHECKBOX,
          					 2, 2, 13, 13, infoPtr->hwndSelf, 0, 
 						(HINSTANCE)GetWindowLongPtrW (infoPtr->hwndSelf, GWLP_HINSTANCE), 0);
-        SendMessageW (infoPtr->hwndCheckbut, BM_SETCHECK, 1, 0);
+        SendMessageW (infoPtr->hwndCheckbut, BM_SETCHECK, infoPtr->dateValid ? 1 : 0, 0);
     }
     if ( (lpss->styleOld & DTS_SHOWNONE) && !(lpss->styleNew & DTS_SHOWNONE) ) {
         DestroyWindow(infoPtr->hwndCheckbut);