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
/**
	 * 
	 * @param schemaName
	 */
	private void getSpecificSchema( String schemaName )
	{
		if ( !isPageInitialization )
		{
			if ( schemaName.equals( JdbcPlugin.getResourceString( "tablepage.text.All" ) )
					|| schemaName.trim( ).length( ) == 0 )
			{
				getAvailableSchema( );
				setMessage( DEFAULT_MESSAGE );
				return;
			}
			if ( containsTableInSchema( schemaName ) )
			{
				schemaList = new ArrayList( );
				schemaList.add( schemaName );
				setMessage( DEFAULT_MESSAGE );
			}
			else
			{
				schemaList = null;
				setMessage( JdbcPlugin.getResourceString( "dataset.editor.page.query.error.schemaNotExisted" ),
						WARNING );
			}
		}
		else
		{