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/provider/JdbcMetaDataProvider.java
metaData = null;
	}
	
	/**
	 * @return Returns the jdbcConnection.
	 */
	public Connection getJdbcConnection() {
		return jdbcConnection;
	}
	
	/**
	 * @param connection The jdbcConnection to set.
	 */
	public void setJdbcConnection(Connection jdbcConnection) {
		this.jdbcConnection = jdbcConnection;
	}	
	
	public Connection connect( String userName, String password, String url,
			String driverClass, String odaDriverName )
	{
        if( url == null || driverClass == null)
        {
            return null;
        }
		if( ( userName != null && !userName.equals(this.userName))  ||  !url.equals(this.url) || !driverClass.equals(this.driverClass))
		{
			if(jdbcConnection != null)
			{
				closeConnection();
				jdbcConnection = null;