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
}
		else
		{
			getSpecificSchema( schemaCombo.getText( ).trim( ) );
		}
		
		
		if ( schemaCombo.getItemCount( ) < 1 )
		{
			schemaCombo.add( JdbcPlugin.getResourceString( "tablepage.text.All" ) );
			schemaCombo.select( 0 );
			if ( schemaList != null )
			{
				Iterator it = schemaList.iterator( );
				while ( it.hasNext( ) )
					schemaCombo.add( it.next( ).toString( ) );
			}
		}
		ArrayList schemaObjectList = new ArrayList( );
		if ( schemaList != null )
		{
			int numberOfSchema = 0;
			Preferences preferences = JdbcPlugin.getDefault( )
					.getPluginPreferences( );
			if ( preferences.contains( DateSetPreferencePage.USER_MAX_NUM_OF_SCHEMA ) )
			{
				numberOfSchema = preferences.getInt( DateSetPreferencePage.USER_MAX_NUM_OF_SCHEMA );
			}
			else
			{