#7 List.setTrackItem throws an exception

[Gerrit Hohl]

List.setTrackItem throws an exception if the list is not yet visible.
Seems there is problem with the calculation of the visible size for the paging as it isn't yet visible: If the widget wasn't visible before, the property "private Rectangle _size;" is null and not initialized. The result is a NullPointerException:

java.lang.NullPointerException
at jcurses.widgets.Widget.getSize(Widget.java:176)
at jcurses.widgets.List.getVisibleSize(List.java:412)
at jcurses.widgets.List.getPaging(List.java:488)
at jcurses.widgets.List.getPageNumber(List.java:495)
at jcurses.widgets.List.findNextSelectableItem(List.java:436)
at jcurses.widgets.List.setTrack(List.java:581)
at jcurses.widgets.List.setTrackedItem(List.java:570)
... and so on ...