validate email address format

public/API/queries/comments.php

@@ -51,6 +51,10 @@ function newComment($conn, $article, $name, $email, $comment, $hCaptchaResponse)
         return "Failed to verify Captcha";
     }
 
+    if(!filter_var($email, FILTER_VALIDATE_EMAIL)) {
+        return "Invalid email address.";
+    }
+
     $article = $conn->escape_string($article);
     $name = $conn->escape_string($name);
     $email = $conn->escape_string($email);