fix(mixins/HttpProxy): don't fail on missing httpServer

Introduced by 98641631a

Similar to bc7fc750f

Which is the case when instanciated from `xo-server-recover-account`.

@xen-orchestra/mixins/HttpProxy.js

@@ -30,6 +30,13 @@ module.exports = class HttpProxy {
   #app
 
   constructor(app, { httpServer }) {
+    // don't setup the proxy if httpServer is not present
+    //
+    // that can happen when the app is instanciated in another context like xo-server-recover-account
+    if (httpServer === undefined) {
+      return
+    }
+
     this.#app = app
 
     const events = new EventListenersManager(httpServer)

CHANGELOG.unreleased.md

@@ -28,4 +28,5 @@
 >
 > In case of conflict, the highest (lowest in previous list) `$version` wins.
 
+- @xen-orchestra/mixins patch
 - xo-server patch