Don't send SELECTED events for an already selected item in wxGTK wxListBox.

Bring wxGTK in line with wxMSW behaviour and avoid sending the
wxEVT_COMMAND_LISTBOX_SELECTED events when the user clicks on an already
selected item.

Refactor wxMSW code to extract the logic to avoid such events into a reusable
in other ports wxListBoxBase::DoChangeSingleSelection() function. Also add
wxListBox::GTKOnSelectionChanged() to wxGTK to avoid having to make the new
function public just so that it could be called by GTK callback and make the
previously existing CalcAndSendEvent() protected as well.

This fixes a unit test failure in ListBoxTestCase::ClickEvents() under wxGTK.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65935 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/listbox.cpp

@@ -689,20 +689,10 @@ bool wxListBox::MSWCommand(WXUINT param, WXWORD WXUNUSED(id))
     if ( n == wxNOT_FOUND )
        return false;
 
-    // As we don't use m_oldSelections in single selection mode, we store the
-    // last item that we notified the user about in it in this case because we
-    // need to remember it to be able to filter out the dummy LBN_SELCHANGE
-    // messages that we get when the user clicks on an already selected item.
     if ( param == LBN_SELCHANGE )
     {
-        if ( !m_oldSelections.empty() && *m_oldSelections.begin() == n )
-        {
-            // Same item as the last time.
+        if ( !DoChangeSingleSelection(n) )
             return false;
-        }
-
-        m_oldSelections.clear();
-        m_oldSelections.push_back(n);
     }
 
     // Do generate an event otherwise.