Prevent NULL from being passed to strlen()

Problem/Motivation

If NULL is passed to _name_format_add_component(), it will eventually make its way to strlen(), which raises a deprecation message in PHP 8.0. The first conditional in _name_format_apply_modifiers() appears to be written incorrectly.

Proposed resolution

In _name_format_apply_modifiers(), only operate on values that are non-empty strings.