use ternary op to send copyright text to songlist component

+ return a zeros if seconds is undefined in formatSeconds()

src/views/FolderView.vue

@@ -15,7 +15,7 @@
       <SongList
         :tracks="FStore.tracks"
         :path="FStore.path"
-        :copyright="() => null"
+        :copyright="null"
       />
     </div>
   </div>

src/views/album/Content.vue

@@ -6,13 +6,7 @@
         :tracks="disc"
         :on_album_page="true"
         :disc="key"
-        :copyright="
-          () => {
-            if (isLastDisc(key)) {
-              return copyright;
-            }
-          }
-        "
+        :copyright="isLastDisc(key) ? () => copyright : null"
       />
     </div>
   </div>