Bug 153378 [Regression]Label text won't show up when the text key is not found
Steps to reproduce: 1.Add a label, set text to "aaa" 2.Add a resource file "a" to the report, add a text key "k1" which is not in the a.properties to the label 3.Preview in Web Viewer Expected result: Label display "aaa" when the text key is not found Actual result: Nothing in preview
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/core/ReferencableStructure.java
* 
	 * @see org.eclipse.birt.report.model.core.IReferencable#addClient(org.eclipse.birt.report.model.core.DesignElement,
	 *      java.lang.String)
	 */
	public void addClient( DesignElement client, String propName )
	{
		clients.add( new BackRef( client, propName ) );
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.birt.report.model.core.IReferencable#dropClient(org.eclipse.birt.report.model.core.DesignElement)
	 */
	public void dropClient( DesignElement client )
	{
		for ( int i = 0; i < clients.size( ); i++ )
		{
			if ( ( (BackRef) clients.get( i ) ).element == client )
			{
				clients.remove( i );
				return;
			}
		}
		assert false;
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.birt.report.model.core.IReferencable#getClientList()
	 */