Show error message when visit profile page of invalid user

src/components/user_profile/user_profile.js

@@ -4,6 +4,11 @@ import Timeline from '../timeline/timeline.vue'
 import FollowList from '../follow_list/follow_list.vue'
 
 const UserProfile = {
+  data () {
+    return {
+      error: false
+    }
+  },
   created () {
     this.$store.commit('clearTimeline', { timeline: 'user' })
     this.$store.commit('clearTimeline', { timeline: 'favorites' })
@@ -13,6 +18,9 @@ const UserProfile = {
     this.startFetchFavorites()
     if (!this.user.id) {
       this.$store.dispatch('fetchUser', this.fetchBy)
+        .catch(() => {
+          this.error = true
+        })
     }
   },
   destroyed () {

src/components/user_profile/user_profile.vue

@@ -55,7 +55,8 @@
       </div>
     </div>
     <div class="panel-body">
-      <i class="icon-spin3 animate-spin"></i>
+      <span v-if="error">{{ $t('user_profile.profile_does_not_exist') }}</span>
+      <i class="icon-spin3 animate-spin" v-else></i>
     </div>
   </div>
 </div>