fix(ui): serve the placeholder for known-absent art instead of a broken icon

getCoverArtUrl returned '' for an imageAbsent record, so <img src={undefined}> rendered as the browser's broken-image icon on every absent cover. The server already serves a proper placeholder for absent art, so build the url and let it render.

ui/src/subsonic/index.js

@@ -81,10 +81,6 @@ const getAvatarUrl = (username, size) =>
   )
 
 const getCoverArtUrl = (record, size, square) => {
-  // Known-absent art would only ever return a placeholder; skip the round trip entirely.
-  if (record.imageAbsent) {
-    return ''
-  }
   const suffix = record.imageHash ? '_' + record.imageHash : ''
   const options = {
     // A hash-suffixed url is already pixel-versioned; the buster would defeat immutable caching.

ui/src/subsonic/index.test.js

@@ -151,14 +151,15 @@ describe('getCoverArtUrl', () => {
     expect(url).toContain('_=')
   })
 
-  it('returns an empty url for known-absent artwork', () => {
-    expect(
-      subsonic.getCoverArtUrl({
-        id: 'album-123',
-        albumArtist: 'AA',
-        imageAbsent: true,
-      }),
-    ).toBe('')
+  it('still builds a url for known-absent artwork so the server placeholder renders', () => {
+    // Returning '' here made <img src=undefined> render as a broken icon; the server serves a
+    // proper placeholder for absent art, so the client must still request it.
+    const url = subsonic.getCoverArtUrl({
+      id: 'album-123',
+      albumArtist: 'AA',
+      imageAbsent: true,
+    })
+    expect(url).toContain('al-album-123')
   })
 })