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/ExtensionLoader.java
*            the property tag
		 * @param elementDefn
		 *            element definition
		 * @throws ExtensionException
		 *             if the class some attribute specifies can not be
		 *             instanced.
		 */
		void loadPropertyVisibility( IConfigurationElement propTag,
				ExtensionElementDefn elementDefn ) throws ExtensionException
		{
			
			String name = propTag.getAttribute( NAME_ATTRIB );
			checkRequiredAttribute( NAME_ATTRIB, name );
			
			String visible = propTag.getAttribute( VISIBILITY_ATTRIB );
			elementDefn.addPropertyVisibility( name, visible );
		}
		/**
		 * Loads the properties of one group.
		 * 
		 * @param elementTag
		 *            the element tag
		 * @param propGroupTag
		 *            the property group tag
		 * @param elementDefn
		 *            element definition
		 * @param propList
		 *            the property list into which the new property is added.
		 * 
		 * @throws MetaDataException