use custom selection colours in wxHtmlListBox again (restores functionality broken by patch 1650804 in r44640)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@52264 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/vlbox.h

@@ -269,6 +269,14 @@ protected:
     // common part of keyboard and mouse handling processing code
     void DoHandleItemClick(int item, int flags);
 
+    // paint the background of the given item using the provided colour if it's
+    // valid, otherwise just return false and do nothing (this is used by
+    // OnDrawBackground())
+    bool DoDrawSolidBackground(const wxColour& col,
+                               wxDC& dc,
+                               const wxRect& rect,
+                               size_t n) const;
+
 private:
     // the current item or wxNOT_FOUND
     //