Closes:#11

gpm_stats_notebook_changed_cb is invoked through a callback in gpm_stats_update_info_data when changing to a device if that device has a different number of history/statistics pages when the widget is hidden. As the gpm_stats_notebook_changed_cb is called by itself it creates a condition when hiding the middle tab (position 1) where all the tabs are hidden and there is nothing to show.

If there are any instances of the 'switch-page' callback that don't also have a 'changed' or 'notify' from the tree view it could theoretically be possible to have history & statistics tabs shown where not necessary. This would be mitigated by the tabs showing that there was no data to display.