Avoid throwing exception when receiving invalid SqlNotificationInfo value

[johnnypham]

Addresses #1376

When receiving an invalid SqlNotificationInfo value, an exception would be thrown because the call to Enum.Parse fails. We can use Enum.TryParse to avoid this. The result will still be SqlNotificationInfo.Unknown either way.

[ascott18]

I can confirm after testing that the exception is no longer thrown. The "none" attribute value still comes out as "Unknown" as expected, but without having VS break into an exception when exception settings are all enabled and Just My Code is disabled.

[cheenamalhotra]

Can you add a test case here to cover this code block?

[johnnypham]

Can you add a test case here to cover this code block?

I was unable to reproduce it but this is a server-side bug so it shouldn't be occurring. If it does, we'll avoid throwing an unnecessary exception.