Bug 142939 Invalid interval will cause incorrect group action.
Description: Invalid interval will cause incorrect group action. Steps to reproduce: 1. Insert a list 2. Add a group, key is string type column, set interval to year, range to 3 3. Preview Expected result: Error msg about invald interval and ignore the invalid interval. Actual result: No error msg and only return one group with all datarows.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/impl/QueryExecutor.java
if ( ( src.getInterval( ) != IGroupDefinition.NO_INTERVAL )
						&& ( src.getIntervalRange( ) != 0 ) )
				{
					try
					{
						expr = ExpressionUtil.createGroupByExpression( src.getInterval( ),
								src.getIntervalStart( ),
								getGroupKeyExpression( src ),
								src.getIntervalRange( ) );
						
					}
					catch(BirtException be)
					{
						throw DataException.wrap( be );
					}
				}
				IQuery.GroupSpec dest = QueryExecutorUtil.groupDefnToSpec( cx,
						src,
						expr,
						groupName,
						-1 );
				groupSpecs[i] = dest;
				if ( ( dest.getInterval( ) != IGroupDefinition.NO_INTERVAL )
						&& ( dest.getIntervalRange( ) != 0 ) )
				{
					if (dest.getInterval( ) == IGroupDefinition.STRING_PREFIX_INTERVAL)
					{
						temporaryComputedColumns.add( new ComputedColumn( groupName,
								expr,
								DataType.STRING_TYPE ) );