refs #16883 [finc] show hierarchy tree tab only if there actually is a hierarchy tree to show

* do not show tab for single-element trees

module/finc/src/finc/RecordTab/HierarchyTree.php

@@ -51,17 +51,20 @@ class HierarchyTree extends \VuFind\RecordTab\HierarchyTree
         else return 'hierarchy_tree';
     }
 
-    /**
-     * {@inheritdoc}
-     * Returns different descriptions according to record type
-     * @return string
-     */
-/*    public function isActive()
+    public function isActive()
     {
-        return (
-            $this->getRecordDriver()->tryMethod('isSingleElementHierarchyRecord')
-                ? false : parent::isActive()
-        );
+        $trees = $this->getTreeList();
+        if (empty($trees)) {
+            return false;
+        }
+        foreach ($trees as $key => $value) {
+            if ($key !== $this->driver->getUniqueID()) {
+                return true;
+            }
+        }
+        if ($this->driver->getChildRecordCount() > 0) {
+            return true;
+        }
+        return false;
     }
-*/
 }