return bool is_error with http response (#558)

* let the HTTP request function return an error with boolean is_error so the toasts can be shown correctly even when there is no return value from the backend

static/js/http.js

@@ -15,9 +15,9 @@ function request (method, path, options = {}) {
   return window.fetch(path, opts)
     .then(response => {
       if (!response.ok) {
-        const error = { status: response.status, reason: response.statusText }
+        const error = { status: response.status, reason: response.statusText, is_error: true }
         return response.json()
-          .then(json => { error.reason = json.reason })
+          .then(json => { error.reason = json.reason; return error })
           .finally(() => { standardErrorHandler(error) })
       } else { return response.json().catch(() => null) }
     })

static/js/queues.js

@@ -125,7 +125,8 @@ document.querySelector('#declare').addEventListener('submit', function (evt) {
     arguments: Dom.parseJSON(data.get('arguments'))
   }
   HTTP.request('PUT', url, { body })
-    .then(() => {
+    .then((response) => {
+      if (response?.is_error) { return }
       queuesTable.reload()
       evt.target.reset()
       Dom.toast('Queue ' + queue + ' created')