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/ElementDefn.java
* Whether this element acts as a container. If so, which slots it
	 * implements.
	 */
	protected ArrayList slots = null;
	/**
	 * Whether this element can be extended. If true, elements of this type can
	 * extend from another element of the same type. If false, elements cannot
	 * extend.
	 */
	protected boolean allowExtend = true;
	/**
	 * Determines which class that this element belongs to.
	 */
	protected String javaClass = null;
	/**
	 * The collection of semantic validation trigger definition.
	 */
	private SemanticTriggerDefnSet triggerDefnSet = null;
	/**
	 * The list contains the information that how the property sheet shows an
	 * property for an extension element.
	 */
	protected Map propVisibilites = null;
	/**
	 * The name of the XML element used when serializing this ROM element.
	 */
	protected String xmlName;
	/**
	 * Cached property definitions. It contains local defined and parents'
	 * defined property definitions. After parsing ROM, property definition