html: better HTTP return code for malformed id in /scan:id

Signed-off-by: Davide Madrisan <davide.madrisan@gmail.com>

html/server/routes/scan.js

@@ -52,7 +52,7 @@ module.exports = function(wagner) {
                 }
                 catch(error) {
                     return res.
-                        status(HTTPStatus.INTERNAL_SERVER_ERROR).
+                        status(HTTPStatus.BAD_REQUEST).
                         json({ error: error.message });
                 }