[web-src] Always show cover artwork in album dialog

If no artwork is available or not yet loaded, falls back to the
generated cover artwork. Avoids jumping of dialog after loading of
remote image finished.

web-src/src/pages/PageNowPlaying.vue

@@ -2,19 +2,11 @@
   <section>
     <div v-if="now_playing.id > 0" class="fd-is-fullheight">
       <div class="fd-is-expanded">
-        <figure @click="open_dialog(now_playing)" class="fd-cover-image">
-          <img
-            v-show="artwork_visible"
-            :src="artwork_url"
-            class="fd-has-action"
-            @load="artwork_loaded"
-            @error="artwork_error">
-          <cover-placeholder
-            v-show="!artwork_visible"
-            :artist="now_playing.artist"
-            :album="now_playing.album"
-            class="fd-has-action" />
-        </figure>
+        <cover-artwork @click="open_dialog(now_playing)"
+          :artwork_url="now_playing.artwork_url"
+          :artist="now_playing.artist"
+          :album="now_playing.album"
+          class="fd-cover-image fd-has-action" />
       </div>
       <div class="fd-has-padding-left-right">
         <div class="container has-text-centered">
@@ -68,19 +60,18 @@
 <script>
 import ModalDialogQueueItem from '@/components/ModalDialogQueueItem'
 import RangeSlider from 'vue-range-slider'
-import CoverPlaceholder from '@/components/CoverPlaceholder'
+import CoverArtwork from '@/components/CoverArtwork'
 import webapi from '@/webapi'
 import * as types from '@/store/mutation_types'
 
 export default {
   name: 'PageNowPlaying',
-  components: { ModalDialogQueueItem, RangeSlider, CoverPlaceholder },
+  components: { ModalDialogQueueItem, RangeSlider, CoverArtwork },
 
   data () {
     return {
       item_progress_ms: 0,
       interval_id: 0,
-      artwork_visible: false,
 
       show_details_modal: false,
       selected_item: {}
@@ -113,10 +104,6 @@ export default {
       return this.$store.getters.now_playing
     },
 
-    artwork_url: function () {
-      return webapi.artwork_url_append_size_params(this.now_playing.artwork_url)
-    },
-
     settings_option_show_composer_now_playing () {
       return this.$store.getters.settings_option_show_composer_now_playing
     },
@@ -150,14 +137,6 @@ export default {
       })
     },
 
-    artwork_loaded: function () {
-      this.artwork_visible = true
-    },
-
-    artwork_error: function () {
-      this.artwork_visible = false
-    },
-
     open_dialog: function (item) {
       this.selected_item = item
       this.show_details_modal = true