message: Add default string for popup menu filter expression.
diff: @@ -1306,6 +1306,8 @@ TraceWin::TraceWin( TraceLoader &loader, TraceEvents *trace_events, std::string
  strcpy_safe( m_timegoto_buf, "0.0" );
  strcpy_safe( m_timeoffset_buf, "0.0" );
  + strcpy_safe( m_new_graph_row_buf, "<Enter Filter Expression>" );
  +
  std::string event_filter = m_loader.m_inifile.GetStr( "event_filter_buf", "" );
  if ( !event_filter.empty() )
  {
  