Clean up error object to be consistent with dicomweb-client.
Clean up error object to be consistent with dicomweb-client.

chafey/cornerstoneWADOImageLoader,cornerstonejs/cornerstoneWADOImageLoader,cornerstonejs/cornerstoneWADOImageLoader,cornerstonejs/cornerstoneWADOImageLoader,chafey/cornerstoneWADOImageLoader,chafey/cornerstoneWADOImageLoader