improve get_code function

src/routes/(angemeldet)/upload/+page.svelte

@@ -195,13 +195,15 @@
 	}
 
 	async function get_code(case_no) {
-		let url = `/api/list/${case_no}/code`
+		if (case_no == '') return;
+
+		let url = `/api/list/${case_no}/code`;
 		const response = await fetch(url);
 
 		if (response.status == 200) {
 			return response.text();
 		} else {
-			return -1
+			return -1;
 		}
 	}