Gracefully handle audio updates api returning 204

[ahmedre]

When there are no updates, the audio updates api returns 204. Gracefully
handle this by treating null as no data.

[github-actions]

OLD: app-madani-debug.apk (signature: V1, V2)
NEW: app-madani-debug.apk (signature: V1, V2)

          │          compressed           │         uncompressed          
          ├───────────┬───────────┬───────┼───────────┬───────────┬───────
 APK      │ old       │ new       │ diff  │ old       │ new       │ diff  
──────────┼───────────┼───────────┼───────┼───────────┼───────────┼───────
      dex │  24.2 MiB │  24.2 MiB │ +56 B │  74.8 MiB │  74.8 MiB │ +64 B 
     arsc │   2.7 MiB │   2.7 MiB │   0 B │   2.7 MiB │   2.7 MiB │   0 B 
 manifest │   5.8 KiB │   5.8 KiB │   0 B │    28 KiB │    28 KiB │   0 B 
      res │   1.7 MiB │   1.7 MiB │   0 B │     2 MiB │     2 MiB │   0 B 
   native │  18.8 KiB │  18.8 KiB │   0 B │  36.5 KiB │  36.5 KiB │   0 B 
    asset │ 404.2 KiB │ 404.2 KiB │   0 B │ 678.6 KiB │ 678.6 KiB │   0 B 
    other │ 218.3 KiB │ 218.3 KiB │  -1 B │ 464.6 KiB │ 464.6 KiB │   0 B 
──────────┼───────────┼───────────┼───────┼───────────┼───────────┼───────
    total │  29.2 MiB │  29.2 MiB │ +55 B │  80.6 MiB │  80.6 MiB │ +64 B