Bug 294738 [Viewers] (JFace) Assertion for missing LabelProvider in ViewerColumn
ViewerColumn should throw an AssertionException if the LabelProvider is missing for a column to provide a helpful error message.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/ViewerColumn.java
*            the widget owning the viewer in case the widget has no columns
	 *            this could be the widget itself
	 */
	protected ViewerColumn(final ColumnViewer viewer, Widget columnOwner) {
		this.viewer = viewer;
		columnOwner.setData(ViewerColumn.COLUMN_VIEWER_KEY, this);
		this.listener = new ILabelProviderListener() {
			public void labelProviderChanged(LabelProviderChangedEvent event) {
				viewer.handleLabelProviderChanged(event);
			}
		};
		columnOwner.addDisposeListener(new DisposeListener() {
			public void widgetDisposed(DisposeEvent e) {
				handleDispose(viewer);
			}
		});
	}
	/**
	 * Return the label provider for the receiver.
	 * 
	 * @return ViewerLabelProvider
	 */
	CellLabelProvider getLabelProvider() {
		return labelProvider;
	}
	/**
	 * Set the label provider for the column. Subclasses may extend but must
	 * call the super implementation.
	 * 
	 * @param labelProvider