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
return null;
	}
	
	/*
	 *  (non-Javadoc)
	 * @see org.eclipse.birt.report.data.oda.jdbc.ui.provider.IMetadataProvider#getCrossReferences(java.lang.String, java.lang.String, java.lang.String, java.lang.String)
	 */
	{
		{
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		{
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		{
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		{
				
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			}
			}
		}
		{
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	}
	/**
	 * When using some driver, one connection metaData can only use methods like