Fix an instance of strlen(null)

Summary: Ref Q112, ref T15064.

Test Plan:
Enter the text `[[hello]]` in a remarkup field - without this change, it causes a deprecation warning in the log.

This doesn't happen if the content looks like a valid URL - this is the "Wiki Link" syntax.

Reviewers: bekay, O1 Blessed Committers, valerio.bozzolan

Reviewed By: O1 Blessed Committers, valerio.bozzolan

Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T15064

Differential Revision: https://we.phorge.it/D25539

src/applications/phriction/markup/PhrictionRemarkupRule.php

@@ -191,7 +191,7 @@ final class PhrictionRemarkupRule extends PhutilRemarkupRule {
 
       // If the name is something meaningful to humans, we'll render this
       // in text as: "Title" <link>. Otherwise, we'll just render: <link>.
-      $is_interesting_name = (bool)strlen($name);
+      $is_interesting_name = phutil_nonempty_string($name);
 
       $target = idx($document_map, $key, null);