fix parameter count for sprintf() in StudipLock::get(), fixes #1247

Closes #1247

Merge request studip/studip!763

lib/classes/StudipLock.class.php

@@ -49,7 +49,10 @@ class StudipLock
     public static function get($lockname, $timeout = 10)
     {
         if (self::$current !== null) {
-            throw new UnexpectedValueException(sprintf('could not acquire new lock, %s still active'));
+            throw new UnexpectedValueException(sprintf(
+                'could not acquire new lock, %s still active',
+                self::$current
+            ));
         }
         $ok = DBManager::get()->fetchColumn("SELECT GET_LOCK(?,?)", [self::lockname($lockname), $timeout]);
         if ($ok) {