Detect invalid access to IsFailure on ServiceResult<T> objects.

[randymarsh77]

Calling .Value on a ServiceResult<T> will call Verify(), which will throw if the result is a failure.

However, this semantic might not be obvious, so a developer might think this is perfectly fine error checking code:

var result = await ServiceResultReturningTask();
var someImportantValue = result.Value?.Property;
if (result.IsFailure || someImportantValue == null)
  ... error case

Instead, this code would throw.

It seems like accessing to the .Value property before accessing the .IsFailure is always a bug, and also detectable.

A common case that is not a bug would be using the Verify() semantic of .Value to throw on failure. In this case, explicitly accessing .IsFailure would not be needed.

[randymarsh77]

Suggested code fixes:

var result = await ServiceResultReturningTask();
if (result.IsFailure || result.Value?.Property == null)
  ... error case

var result = await ServiceResultReturningTask();
var someImportantValue = result.IsFailure ? null : result.Value?.Property;
if (someImportantValue == null)
  ... error case

someImportantValue.useThisObject();