fix: add null-safe relationship lookup

Author: luccas-harbour

packages/super-editor/src/editors/v1/core/super-converter/v2/importer/docxImporter.js

@@ -680,7 +680,7 @@ export function addDefaultStylesIfMissing(styles) {
  */
 const importHeadersFooters = (docx, converter, mainEditor, numbering, translatedNumbering, translatedLinkedStyles) => {
   const rels = docx['word/_rels/document.xml.rels'];
-  const relationships = rels?.elements.find((el) => el.name === 'Relationships');
+  const relationships = rels?.elements?.find((el) => el.name === 'Relationships');
   const elements = relationships?.elements ?? [];
 
   const headerType = 'http://schemas.openxmlformats.org/officeDocument/2006/relationships/header';