fix $thing parameter in deprecation helper

See dokuwiki@615810c#r161070574

Author: splitbrain

inc/Debug/DebugHelper.php

@@ -53,7 +53,7 @@ public static function dbgDeprecatedFunction($alternative = '', $callerOffset =
         self::triggerDeprecationEvent(
             $backtrace,
             $alternative,
-            self::formatCall($self),
+            $thing ?: self::formatCall($self),
             self::formatCall($call),
             $self['file'] ?? $call['file'] ?? '',
             $self['line'] ?? $call['line'] ?? 0