Check item index in wxListCtrl::GetItemState() in wxMSW too

This was already the case in the generic version, but wxMSW one just
silently returned 0 for invalid item index.

Make it consistent with the other platforms and SetItemState() by
checking the index in it too.

Closes https://github.com/wxWidgets/wxWidgets/pull/1702

docs/changes.txt

@@ -87,6 +87,9 @@ Changes in behaviour not resulting in compilation errors
   there is no highlighted menu item, instead of wxID_ANY used before, for
   consistency with wxMSW.
 
+- wxListCtrl::GetItemState() in wxMSW now checks the passed in item index for
+  validity, as the generic version under the other platforms already did.
+
 
 Changes in behaviour which may result in build errors
 -----------------------------------------------------

src/msw/listctrl.cpp

@@ -1077,6 +1077,9 @@ bool wxListCtrl::SetItem(long index, int col, const wxString& label, int imageId
 // Gets the item state
 int wxListCtrl::GetItemState(long item, long stateMask) const
 {
+    wxCHECK_MSG( item >= 0 && item < GetItemCount(), 0,
+                 wxS("invalid list control item index in GetItemState()") );
+
     wxListItem info;
 
     info.m_mask = wxLIST_MASK_STATE;