message: Fix some potential null pointer dereferences
  These two were discovered through clang's scan-build. I don't know
  if they can be triggered in the real world since they do appear to
  rely on certain GUI states which a human may not be able to trigger.
diff: @@ -4287,7 +4287,7 @@ void MainApp::render_color_picker()
  {
  changed |= render_color_picker_colors( m_colorpicker, m_colorpicker_color );
  }
  - else if ( !m_colorpicker_event.empty() )
  + else if ( !m_colorpicker_event.empty() && win )
  {
  changed |= render_color_picker_event_colors( m_colorpicker,
  win, m_colorpicker_event );
  @@ -4309,7 +4309,7 @@ void MainApp::render_color_picker()
  s_textclrs().update_colors();
  }
  - else if ( !m_colorpicker_event.empty() )
  + else if ( !m_colorpicker_event.empty() && win )
  {
  win->m_trace_events.set_event_color( m_colorpicker_event, m_colorpicker.m_color );
  }
  