V9 fixes

[MarkMpn]

Fixed NullReferenceExceptions triggered when:

• executing a conditional SELECT query - fixes NullReferenceException on Exists #462
• retrieving results from a Fetch XML query using IN or EXISTS
• handling an error returned from TDS Endpoint - fixes "Object reference not set to an instance of an object" if a column is not available in tables / subqueries #463
• handling internal errors such as UPDATE without WHERE