Fix for exception when errors returned from Rally.
Fix for exception when errors returned from Rally.

ebsco/RallyRestToolkitFor.NET,RallyTools/RallyRestToolkitFor.NET,ebsco/RallyRestToolkitFor.NET,agibson-fl/RallyRestToolkitFor.NET,RallyTools/RallyRestToolkitFor.NET,agibson-fl/RallyRestToolkitFor.NET