Improve performance of placeholder images (#1325)

* Don't include updatedAt field when fetching album art placeholder. This will allow browers to cache the place holder

* Apply resizing to placeholder image

* Fix issues discovered by CI linter and prettier

* Updates from PR review

ui/src/subsonic/index.js

@@ -49,7 +49,11 @@ const getCoverArtUrl = (record, size) => {
     ...(record.updatedAt && { _: record.updatedAt }),
     ...(size && { size }),
   }
-  return baseUrl(url('getCoverArt', record.coverArtId || 'not_found', options))
+  if (record.coverArtId) {
+    return baseUrl(url('getCoverArt', record.coverArtId, options))
+  } else {
+    return baseUrl(url('getCoverArt', 'not_found', size && { size }))
+  }
 }
 
 const streamUrl = (id) => {