fixes autochangelog erroring on an empty pr body https://github.com/t…

…gstation/tgstation/actions/runs/8977813552/job/24657813451 the changelog workflow errors when theres nothing in the pr body, which causes a useless notification. now it should be fixed (#83122)

tools/pull_request_hooks/changelogParser.js

@@ -64,6 +64,9 @@ function parseChangelogBody(lines, openTag) {
 }
 
 export function parseChangelog(text) {
+	if(text == null) {
+		return undefined;
+	}
 	const lines = text.split("\n").map((line) => line.trim());
 
 	for (let index = 0; index < lines.length; index++) {