Fix crash when req.query handling

https://expressjs.com/en/5x/api.html#req.query

"As req.query’s shape is based on user-controlled input, all properties and values in this object
are untrusted and should be validated before trusting"

In essence, req.query.xx can be an array OR an array of strings.

src/proxyauth.js

@@ -134,7 +134,7 @@ async function login(req, res, next) {
 
     const dashboardFqdn = (await dashboard.getLocation()).fqdn;
 
-    if (req.query.redirect) {
+    if (typeof req.query.redirect === 'string') {
         res.cookie('cloudronProxyAuthRedirect', req.query.redirect, {
             httpOnly: true,
             maxAge: constants.DEFAULT_TOKEN_EXPIRATION_MSECS,
@@ -146,7 +146,7 @@ async function login(req, res, next) {
 }
 
 async function callback(req, res, next) {
-    if (!req.query.code) return next(new HttpError(400, 'missing query argument "code"'));
+    if (typeof req.query.code !== 'string') return next(new HttpError(400, 'missing query argument "code"'));
 
     debug(`callback: with code ${req.query.code}`);