Fix arg to _add_highlight_filter to avoid KeyError

[708yamaguchi]

When I was using rqt_console and tried to do node highlight, I faced the following KeyError.
So I fixed argument to _add_highlight_filter to avoid the KeyError.

$ rqt_console
Traceback (most recent call last):
  File "/home/leus/catkin_workspace/src/rqt_console/src/rqt_console/console_widget.py", line 805, in _handle_mouse_press
    self._rightclick_menu(event)
  File "/home/leus/catkin_workspace/src/rqt_console/src/rqt_console/console_widget.py", line 560, in _rightclick_menu
    action.text(), action.parentWidget().title(), False)
  File "/home/leus/catkin_workspace/src/rqt_console/src/rqt_console/console_widget.py", line 467, in _process_highlight_exclude_filter
    filter_index = self._add_highlight_filter(col)
  File "/home/leus/catkin_workspace/src/rqt_console/src/rqt_console/console_widget.py", line 330, in _add_highlight_filter
    newfilter = self.filter_factory[filter_index][1]()
KeyError: 2
Aborted (core dumped)