fix: login code null submission and login code length check (#1512)

Co-authored-by: james <james@goldfish.net>
Co-authored-by: Kyle Mendell <kmendell@ofkm.us>

frontend/src/routes/login/alternative/code/+page.svelte

@@ -27,6 +27,7 @@
 	});
 
 	async function authenticate() {
+		if (!code?.trim()) return;
 		isLoading = true;
 		try {
 			const user = await userService.exchangeOneTimeAccessToken(code);