don't crash in HiglightAll() (called, in particular, from SortItems()) when the control is empty (patch 1821550)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@49590 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/listctrl.cpp

@@ -2865,9 +2865,10 @@ void wxListMainWindow::HighlightAll( bool on )
             RefreshLine(m_current);
         }
     }
-    else // multi sel
+    else // multi selection
     {
-        HighlightLines(0, GetItemCount() - 1, on);
+        if ( !IsEmpty() )
+            HighlightLines(0, GetItemCount() - 1, on);
     }
 }