Return empty strings for Jira links when URL is not set

Merged Markus Koller requested to merge 334344-jira-blank-web-url into master

What does this MR do?

With the changes in cb4de493 (!63900 (merged)) we started returning nil from methods like Integrations::Jira#issues_url if the URL is not set, which broke certain pages like the project dashboard.

Fixes #334344 (closed).

Does this MR meet the acceptance criteria?

Conformity

Availability and Testing

Related to #334344 (closed)

Edited by Markus Koller