Bug 163018 An error extension will lead the report contain chart can't be opened and can not new a report.
Details: An error extension will lead the report contain chart can't open In org.eclipse.birt.report.tests.model has an error extension. When run the birt use workbenck, the report contain chart can't be opened and it can not new a report.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/metadata/PeerExtensionLoader.java
*            the element tag
		 * @param elementTypeTag
		 *            the element type tag
		 * @param elementDefn
		 *            element definition
		 * @return name of the element type
		 * @throws ExtensionException
		 *             if the class some attribute specifies can not be
		 *             instanced.
		 */
		String loadSlotElementType( IConfigurationElement elementTypeTag )
				throws ExtensionException
		{
			
			String name = elementTypeTag.getAttribute( NAME_ATTRIB );
			checkRequiredAttribute( NAME_ATTRIB, name );
			return name;
		}
		/**
		 * Determines whether the element type is invalid or not. Now only
		 * support(ReportItem, Column, Row, Cell, ListingGroup).
		 * 
		 * @param type
		 *            the type
		 * @return true if the type is valid, otherwise false
		 */
		boolean isValidElementType( String type )
		{
			if ( ReportDesignConstants.EXTENDED_ITEM.equalsIgnoreCase( type )
					|| ReportDesignConstants.COLUMN_ELEMENT