Bug 156166 Error occour when previewing attached report in web viewer.
Decription:Error occour when previewing attached report in web viewer. Steps to reproduce: 1.run attached reports in web viewer. Expeceted results: preview properly Actual results: Error occour when previewing the reports in web viewer while it works properly in html and PDF
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/impl/BindingColumnsEvalUtil.java
{
		private IResultIterator ri;
		private Set columnNameSet;
		
		/**
		 * @param ri
		 */
		private EvalHelper( IResultIterator ri )
		{
			this.ri = ri;
			try
			{
				IResultClass resultClass = ri.getResultClass( );
				
				columnNameSet = new HashSet( );