[#11866] Add error handling for curl response

To test:
 - Pull branch
 - No need for features revert or reinstall
 - Enable dblog module
 - Run a validation test by visiting /wcag-validate-url?url={an invalid url}
 - Check Reports > Recent log messages - There should be an error stating that the WCAG validate module did not return a response.
 - Ensure when visiting the modules page, there are no errors displayed to the user (as per original bug report)