server: don't throw in async callback from index requests

This was flagged as an issue by codeQL

> Server crash [High]
> The server of this route handler will terminate when an
> uncaught exception from this location escapes an
> asynchronous callback.

server/server.ts

@@ -406,22 +406,20 @@ function forceNoCacheRequest(_req: Request, res: Response, next: NextFunction) {
 function indexRequest(_req: Request, res: Response) {
 	res.setHeader("Content-Type", "text/html");
 
-	return fs.readFile(
-		Utils.getFileFromRelativeToRoot("client/index.html.tpl"),
-		"utf-8",
-		(err, file) => {
-			if (err) {
-				throw err;
-			}
+	fs.readFile(Utils.getFileFromRelativeToRoot("client/index.html.tpl"), "utf-8", (err, file) => {
+		if (err) {
+			log.error(`failed to server index request: ${err.name}, ${err.message}`);
+			res.sendStatus(500);
+			return;
+		}
 
-			const config: IndexTemplateConfiguration = {
-				...getServerConfiguration(),
-				...{cacheBust: Helper.getVersionCacheBust()},
-			};
+		const config: IndexTemplateConfiguration = {
+			...getServerConfiguration(),
+			...{cacheBust: Helper.getVersionCacheBust()},
+		};
 
-			res.send(_.template(file)(config));
-		}
-	);
+		res.send(_.template(file)(config));
+	});
 }
 
 function initializeClient(