Fixed missing error for file type validation

index.php

@@ -316,6 +316,7 @@ if (!isset($_POST['submit'])) {
             }
             if (!fileList.length) {
                 submitButton.disabled = true;
+                errorDiv.style.display = 'block';
                 errorDiv.innerHTML += 'Keine gültigen Bilder oder Videos gefunden';
             }
         });