Bug 199021 Error message pops up several times when click an invalid dataset
Description: There is a sqlserver datasource and dataset, remove the jtds driver to let the dataset invalid. Double click on the dataset, the error message will pop up serveral times. Build version:2.2.0.v20070807-0630 Steps to reproduce: 1. Create a sqlserver datasource and dataset. 2. Remove the jtds driver, and the dataset will be invalid. 3. Double click on the dataset. Expect result: Error message pops up once to indicate the problem. Actual result: Error message pops up serveral times.
data/org.eclipse.birt.report.data.oda.jdbc.ui/src/org/eclipse/birt/report/data/oda/jdbc/ui/editors/SQLDataSetEditorPage.java
/**
	 * Adds drop support to viewer.Must set viewer before execution.
	 *  
	 */
	public void addDropSupportToViewer( )
	{
		final StyledText text = viewer.getTextWidget( );
		DropTarget dropTarget = new DropTarget( text, DND.DROP_COPY
				| DND.DROP_DEFAULT );
		dropTarget.setTransfer( new Transfer[]{
			TextTransfer.getInstance( )
		} );
		dropTarget.addDropListener( new DropTargetAdapter( ) {
			public void dragEnter( DropTargetEvent event )
			{
				text.setFocus( );
				if ( event.detail == DND.DROP_DEFAULT )
					event.detail = DND.DROP_COPY;
				if ( event.detail != DND.DROP_COPY )
					event.detail = DND.DROP_NONE;
			}
			public void dragOver( DropTargetEvent event )
			{
				event.feedback = DND.FEEDBACK_SCROLL | DND.FEEDBACK_SELECT;
			}
			public void dragOperationChanged( DropTargetEvent event )
			{
				dragEnter( event );
			}
			public void drop( DropTargetEvent event )