fix: Frontend crash due to invalid citations (#1002)

Author: komalg1

code/frontend/src/components/Answer/AnswerParser.tsx

@@ -19,7 +19,7 @@ export function parseAnswer(answer: AskResponse): ParsedAnswer {
         // Replacing the links/citations with number
         let citationIndex = link.slice(lengthDocN, link.length - 1);
         let citation = cloneDeep(answer.citations[Number(citationIndex) - 1]) as Citation;
-        if (!filteredCitations.find((c) => c.id === citationIndex)) {
+        if (!filteredCitations.find((c) => c.id === citationIndex) && citation !== undefined) {
           answerText = answerText.replaceAll(link, ` ^${++citationReindex}^ `);
           citation.id = citationIndex; // original doc index to de-dupe
           citation.reindex_id = citationReindex.toString(); // reindex from 1 for display