Deselects all items.
<p>
If an item is selected, it is deselected.
If an item is not selected, it remains unselected.
@exception SWTException <ul>
<li>ERROR_THREAD_INVALID_ACCESS when called from the wrong thread
<li>ERROR_WIDGET_DISPOSED when the widget has been disposed
</ul>
Deselects all items. <p> If an item is selected, it is deselected. If an item is not selected, it remains unselected.
@exception SWTException <ul> <li>ERROR_THREAD_INVALID_ACCESS when called from the wrong thread <li>ERROR_WIDGET_DISPOSED when the widget has been disposed </ul>