R1:cf8d5d60a594

Fix a PHP 8.1 deprecated use of strlen with a NULL argument in commit parser

Summary:
With PHP 8.1+ it is not possible to import a commit if the commiter field is not properly defined
Indeed, if the committer 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 T15629

Test Plan:
- Push a commit to an observed subversion…