Fix user listing for users which have neither displayName nor username yet

dashboard/src/views/ActivationView.vue

@@ -86,7 +86,6 @@ onMounted(async () => {
   <div class="container">
     <Transition name="slide-fade" mode="out-in">
       <div v-if="view === VIEWS.OWNER" class="view">
-        <!-- TODO translate -->
         <h1>Welcome to Cloudron</h1>
         <h3>Set up Admin Account</h3>
 

dashboard/src/views/UsersView.vue

@@ -239,7 +239,10 @@ onMounted(async () => {
           <i class="fa fa-ban" v-if="!user.active" v-tooltip="$t('users.users.inactiveTooltip')"></i>
         </template>
         <template #user="user">
-          {{ user.displayName }} &nbsp; <span class="text-muted">{{ user.username }}</span> &nbsp; <i v-show="user.source" class="far fa-address-book" v-tooltip="$t('users.users.externalLdapTooltip')"></i>
+          {{ user.displayName }}
+          <span class="text-muted" style="margin: 0 6px" v-if="user.username">{{ user.username }}</span>
+          <span class="text-muted" style="margin: 0 6px" v-else>{{ user.email }}</span>
+          <i v-show="user.source" class="far fa-address-book" v-tooltip="$t('users.users.externalLdapTooltip')"></i>
         </template>
         <template #groups="user">
           <span class="group-label" v-for="groupId in user.groupIds" :key="groupId">