Fixed media empty permalink errors

[jsorohova]

Problem:
Paperbits throw an error if empty permalink is defined for media files.

Solution:
Checking for empty string before making a request via paperbits.

[github-actions]

Accessibility Insights Action: All applicable checks passed

• URLs: 13 URL(s) passed, and 0 were not scannable
• Rules: 29 check(s) passed, and 23 were not applicable
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This scan used axe-core 4.3.2 with Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/86.0.4240.75 Safari/537.36.