R1:6ec89e9f0866

Fix a PHP 8.1 deprecated use of strlen with a NULL argument

Summary:
With PHP 8.1+ it was not possible to view a commit from subversion repositories.
Indeed, if the commit user and/or email 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.

Note: this may highlight other absurd input values that might be worth correcting
instead…