R1:acfb44d6679e

Fix a PHP 8.1 deprecated use of strlen with a NULL argument on commit page

Summary:
With PHP 8.1+ it is not possible to view a commit if the author field is not properly defined
Indeed, if the commit author is not properly defined, strlen(null) is called, causing a deprecation warning, elevated to exception.
Using strlen() to check string validity is deprecated since PHP 8.1. Phorge adopts phutil_nonempty_string() as a replacement.

Fix T15628

Test Plan:
- Push a new commit on a subversion repository…