fix: Web Validator hangs after supplying non-zip URL #1445

[cka-y]

Summary:

Fix for bug #1445 : Web Validator hangs after supplying non-zip URL

Expected behavior:
Error is displayed when the supplied url is invalid.

Implementation Details:
The load event for XMLHttpRequest is triggered once the request is complete even in the case of server error status code 500 which we send from web/service/controller/ValidationController.
Ref: https://javascript.info/xmlhttprequest

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