Fix list cheats dialog for dark mode

Change unselected item color from white to none in the List Cheats
dialog to fix it for dark mode.

Done with Claude.

Signed-off-by: Rafael Kitover <rkitover@gmail.com>

src/wx/widgets/checkedlistctrl.cpp

@@ -143,7 +143,7 @@ int wxCheckedListCtrl::GetItemImageFromAdditionalState(int addstate)
 wxColour wxCheckedListCtrl::GetBgColourFromAdditionalState(int additionalstate)
 {
     if ((additionalstate & wxLIST_STATE_ENABLED) && this->IsEnabled())
-        return *wxWHITE;
+        return wxNullColour;
 
 #ifdef __WXMSW__
     return wxColour(212, 208, 200);