Shows the item. If the item is already showing in the receiver, this method simply returns. Otherwise, the items are scrolled until the item is visible.
@param item the item to be shown
@exception IllegalArgumentException
- ERROR_NULL_ARGUMENT - if the item is null
- ERROR_INVALID_ARGUMENT - if the item has been disposed
@exception SWTException
- ERROR_WIDGET_DISPOSED - if the receiver has been disposed
- ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver
@see Table#showSelection()