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
* Returns whether this element has the requested slot given the numeric
	 * identifier of the slot.
	 * 
	 * @param slotID
	 *            The slotID to check.
	 * @return True if the slotID exists, false otherwise.
	 */
	public boolean hasSlot( int slotID )
	{
		if ( slots == null )
			return false;
		return slotID >= 0 && slotID < slots.size( );
	}
	/**
	 * Returns the meta-data definition for a slot given its numeric slot
	 * identifier.
	 * 
	 * @param slotID
	 *            The slot identifier.
	 * @return The slot information. Returns null if this element is not a
	 *         container, or if the ID is not valid for this container.
	 */
	public ISlotDefn getSlot( int slotID )
	{
		if ( slots == null )
			return null;
		if ( slotID < 0 || slotID >= slots.size( ) )
			return null;
		return (SlotDefn) slots.get( slotID );
	}