Merge pull request #324 from EreMaijala/jstree-fix

Check in hierarchy tree renderer that the hierarchy title exists in the ...

module/VuFind/src/VuFind/Hierarchy/TreeRenderer/JSTree.php

@@ -92,7 +92,8 @@ class JSTree extends AbstractBase
             $hierarchies = [];
             foreach ($inHierarchies as $hierarchyTopID) {
                 if ($this->getDataSource()->supports($hierarchyTopID)) {
-                    $hierarchies[$hierarchyTopID] = $inHierarchiesTitle[$i];
+                    $hierarchies[$hierarchyTopID] = isset($inHierarchiesTitle[$i])
+                        ? $inHierarchiesTitle[$i] : '';
                 }
                 $i++;
             }