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
numberOfSchema = DateSetPreferencePage.DEFAULT_MAX_NUM_OF_SCHEMA;
				preferences.setValue( DateSetPreferencePage.USER_MAX_NUM_OF_SCHEMA,
						numberOfSchema );
			}
			
			cachedSchemaComboIndex = schemaCombo.getSelectionIndex( );
			if ( schemaCombo.getSelectionIndex( ) < 0 )
			{
				String schemaName = schemaCombo.getText( ).trim( );
				
				if(schemaName.length( )!=0)
				{
					DbObject schemaObj = new DbObject( schemaName,
							schemaName,
							DbObject.SCHEMA_TYPE,
							schemaImage );
					schemaObjectList.add( schemaObj );
				}
				else 
					schemaCombo.select( 0 );
			}
			
			if ( schemaCombo.getSelectionIndex( ) == 0 )
			{
				for ( int i = 0, count = 0; i < schemaList.size( )
						&& count < numberOfSchema; i++ )
				{
					String schemaName = (String) schemaList.get( i );
					if ( containsTableInSchema( schemaName ) )
					{