qa: Don't fail if no scenario + don't show menu item

qa/ui/src/lib/components/Header.svelte

@@ -23,6 +23,7 @@
  } from '@sveltestrap/sveltestrap';
 
  import { auth, gitlab, version } from '$lib/stores/auth';
+ import { themes } from '$lib/stores/themes';
 
  export let activemenu = "";
  $: {
@@ -50,6 +51,7 @@
                 <span class="d-none d-md-inline">Accueil</span>
             </NavLink>
         </NavItem>
+        {#if $themes.length}
         <NavItem>
             <NavLink
                 href="themes"
@@ -59,6 +61,7 @@
                 <span class="d-none d-md-inline">Scénarios</span>
             </NavLink>
         </NavItem>
+        {/if}
         <NavItem>
             <NavLink
                 href="exercices"

qa/ui/src/lib/themes.js

@@ -23,7 +23,12 @@ export class Theme {
 export async function getThemes() {
   const res = await fetch(`api/themes`, {headers: {'Accept': 'application/json'}})
   if (res.status == 200) {
-    return (await res.json()).map((t) => new Theme(t));
+    const data = await res.json();
+    if (data) {
+      return data.map((t) => new Theme(t));
+    } else {
+      return [];
+    }
   } else {
     throw new Error((await res.json()).errmsg);
   }