Prevent crash in case nothing is selected

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_4_BRANCH@19573 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/checklst.cpp

@@ -408,15 +408,19 @@ void wxCheckListBox::OnKeyDown(wxKeyEvent& event)
     if ( oper != None )
     {
         wxArrayInt selections;
-        int count;
+        int count = 0;
         if ( HasMultipleSelection() )
         {
             count = GetSelections(selections);
         }
         else
         {
-            count = 1;
-            selections.Add(GetSelection());
+            int sel = GetSelection();
+            if (sel != -1)
+            {
+                count = 1;
+                selections.Add(sel);
+            }
         }
 
         for ( int i = 0; i < count; i++ )