Bug 151959 inappropriate screen operation
steps to reproduce: - create a report - add a grid item (3x3) - switch to Outline view - expand the grid item to see its rows and cells - select the grid item, and drag it into any of its own cell expected behavior: - is it an invalid screen operation? if it is, it should be banned actual behavior: - the grid item was disappeared surprisingly
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/core/DesignElement.java
* <li>USER_LABEL: Only the first 3 steps can be visited, if not found,
	 * return null</li>
	 * <li>SHORT_LABEL: All the above 5 steps can be visited. This will ensure
	 * there will be a return value</li>
	 * <li>FULL_LABEL: Besides the return value of SHORT_LABEL, this option
	 * says we need to return additional information. To get this, every child
	 * element needs to overwrite this method</li>
	 * </ul>
	 * 
	 * @param module
	 *            the module
	 * @param level
	 *            the description level.
	 * @return the display label of this element.
	 */
	public String getDisplayLabel( Module module, int level )
	{
		
		String displayLabel = ModelUtil.searchForExternalizedValue( this,
				DISPLAY_NAME_ID_PROP, ThreadResources.getLocale( ) );
		
		
		if ( StringUtil.isBlank( displayLabel ) )
		{
			displayLabel = getDisplayName( );
		}
		
		
		
		if ( StringUtil.isBlank( displayLabel ) )