User error message when label retrieval fails

[nuest]

See // TODO: Implement that the user gets notified, that the fetching of the Labels didn't work in file classes/CodecheckRegister/CodecheckVenueNames.php

Related User Stories

• C-AD1 (related): As a codechecker, I want the plugin to automatically reserve a certificate identifier, create the Register issue...
• U-PR1 (related): As any user, I want CODECHECK-related pages to respond quickly...

User story references from the CHECK-PUB User Stories document.

[dxL1nus]

I have implemented this now. When the fetch URL does not exist, the user will get the following error message:

This happens when the PHP curl_exec() function fails

[dxL1nus]

This issue will be closed by PR #79 as well.