DVPL-5287 : C# SDK - Swallow ObjectDisposedException in SearchResultStream

If you dispose, you get no notification that the enumeration ended
prematurely. All other errors originating with the awaited are reported
with the exception thrown by the awaiter:

{code}
throw this.awaiter.LastError;
{code}
Merge branch 'develop' of https://github.com/splunk/splunk-sdk-csharp-pcl into dnoble/refactor