Better error message for invalid response blob (#43069)

Summary:
Pull Request resolved: #43069

Changelog:
[General][Changed] - Add info to invalid blob response error

Reviewed By: christophpurrer

Differential Revision: D53829400

fbshipit-source-id: 17b1dbb3cacf8368098b0b639e8d10aa9bd28d03

Author: Thomas Nardone

packages/react-native/Libraries/Network/XMLHttpRequest.js

@@ -248,7 +248,10 @@ class XMLHttpRequest extends (EventTarget(...XHR_EVENTS): any) {
         } else if (this._response === '') {
           this._cachedResponse = BlobManager.createFromParts([]);
         } else {
-          throw new Error(`Invalid response for blob: ${this._response}`);
+          throw new Error(
+            'Invalid response for blob - expecting object, was ' +
+              `${typeof this._response}: ${this._response}`,
+          );
         }
         break;