Fix JS error on empty citations list.

js/plugins/reference_footnotes/dialogs/footnotes.js

@@ -14,7 +14,7 @@
                           {
                             id: 'reference',
                             type: 'select',
-                            items: [[" - None - ", 0]].concat(drupalSettings.bibcite_footnotes.references),
+                            items: [[" - None - ", 0]].concat(typeof(drupalSettings.bibcite_footnotes) !== 'undefined' ? drupalSettings.bibcite_footnotes.references : []),
                             label: Drupal.t('Reference Footnote item:'),
                             setup: function (element) {
                               if (isEdit)