Add missing function comment

MD_STD_IN.php

@@ -9,7 +9,6 @@
  * functions.
  */
 final class MD_STD_IN {
-
     /**
      * Validates and sanitizes input integers to be in line with MySQL
      * autoincrement IDs.
@@ -231,5 +230,4 @@ public static function validate_isbn(string $input):string {
         throw new MDgenericInvalidInputsException("ISBNs must be either 10 or 13 characters long.");
 
     }
-
 }