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

Please make sure these boxes are checked before submitting your pull request - thanks!

• Run the unit tests with gradle test to make sure you didn't break anything
• Format the title like "feat: [new feature short description]". Title must follow the Conventional Commit Specification(https://www.conventionalcommits.org/en/v1.0.0/).
• Linked all relevant issues
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