[BUGFIX] Fix npe when multiViewAddSource class does not exist (kitodo#1759)

Co-authored-by: Sebastian Meyer <sebastian.meyer@opencultureconsulting.com>

Author: markusweigelt

Configuration/TypoScript/setup.typoscript

@@ -67,7 +67,7 @@ page {
     kitodo-pageView-searchInDocument = EXT:dlf/Resources/Public/JavaScript/PageView/SearchInDocument.js
     kitodo-pageView-pageView = EXT:dlf/Resources/Public/JavaScript/PageView/PageView.js
     kitodo-pageView-teiParser = EXT:dlf/Resources/Public/JavaScript/PageView/TeiParser.js
-    kitodo-pageview-multiViewAddSource = EXT:dlf/Resources/Public/JavaScript/MultiView/MultViewAddSource.js
+    kitodo-pageview-multiViewAddSource = EXT:dlf/Resources/Public/JavaScript/MultiView/MultiViewAddSource.js
     kitodo-search-suggest = EXT:dlf/Resources/Public/JavaScript/Search/Suggester.js
   }
 }

Resources/Public/JavaScript/MultiView/MultViewAddSource.js

@@ -0,0 +1,28 @@
+/**
+ * (c) Kitodo. Key to digital objects e.V. <contact@kitodo.org>
+ *
+ * This file is part of the Kitodo and TYPO3 projects.
+ *
+ * @license GNU General Public License version 3 or later.
+ * For the full copyright and license information, please read the
+ * LICENSE.txt file that was distributed with this source code.
+ */
+
+const multiViewAddSource = document.querySelector('.multiViewAddSource');
+if (multiViewAddSource) {
+  document.querySelector('.multiViewAddSource').addEventListener('submit', function (e) {
+    e.preventDefault();
+    const url = new URL(window.location.href);
+    const params = [...url.searchParams.keys()];
+    const multiview = params.filter(p => p.startsWith("tx_dlf[multiview]"));
+    if (multiview.length === 0) {
+      url.searchParams.append("tx_dlf[multiview]", 1);
+    }
+    const multiViewSources = params.filter(p => p.startsWith("tx_dlf[multiViewSource]["));
+    const nextIndex = multiViewSources.length;
+    const urlValue = document.getElementById('location-field').value.trim();
+    url.searchParams.append(`tx_dlf[multiViewSource][${nextIndex}]`, urlValue);
+    // eslint-disable-next-line
+    window.location.href = url.toString();
+  });
+}