Bug 267117 [JFace] Provide possibility for subclasses to check if a column is visible in ViewerRow
Currently this is decided by checking with width but this makes Nebula-Grid fail.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/ViewerRow.java
/**
	 * Return the bounds for the whole item.
	 * 
	 * @return {@link Rectangle}
	 */
	public abstract Rectangle getBounds();
	/**
	 * Return the item for the receiver.
	 * 
	 * @return {@link Widget}
	 */
	public abstract Widget getItem();
	/**
	 * Return the number of columns for the receiver.
	 * 
	 * @return the number of columns
	 */
	public abstract int getColumnCount();
	/**
	 * Return the image at the columnIndex.
	 * 
	 * @param columnIndex
	 * @return {@link Image} or <code>null</code>
	 */
	public abstract Image getImage(int columnIndex);
	/**
	 * Set the image at the columnIndex
	 * 
	 * @param columnIndex
	 * @param image