Fix PHP 8.1 "strlen(null)" exception in PhabricatorPasteLanguageTransaction.php

Summary:
`strlen()` was used in Phabricator to check if a generic value is a non-empty string.
This behavior 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 of just ignoring. If phutil_nonempty_string() throws an exception in your
instance, report it to Phorge to evaluate and fix that specific corner case.

Closes T15808

Test Plan: Unknown. Given that the function rendering `$value` is later called to construct a title string passed to `pht()` I assume that it should be a string and not a scalar.

Reviewers: O1 Blessed Committers, speck

Reviewed By: O1 Blessed Committers, speck

Subscribers: speck, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T15808

Differential Revision: https://we.phorge.it/D25611

src/applications/paste/xaction/PhabricatorPasteLanguageTransaction.php

@@ -14,7 +14,7 @@ final class PhabricatorPasteLanguageTransaction
   }
 
   private function renderLanguageValue($value) {
-    if (!strlen($value)) {
+    if (!phutil_nonempty_string($value)) {
       return $this->renderValue(pht('autodetect'));
     } else {
       return $this->renderValue($value);