Fix smart & default subtitle selection logic (#579)

## Description
Fixes the logic for subtitle selection when using `Smart` or `Default`
server modes. Also takes into account unknown languages.

This is heavily inspired by [the server selection
logic](https://github.com/jellyfin/jellyfin/blob/release-10.11.z/Emby.Server.Implementations/Library/MediaStreamSelector.cs).
For better or for worse, Wholphin implements this client side.

### Related issues
Fixes #570

.github/workflows/pr.yml

@@ -43,7 +43,7 @@ jobs:
       - name: Build app
         id: buildapp
         run: |
-          ./gradlew clean assembleDebug --no-daemon
+          ./gradlew clean assembleDebug testDebugUnitTest --no-daemon
           apks=$(find app/build/outputs/apk -name '*.apk' -print0 | tr '\0' ',' | sed 's/,$//')
           echo "apks=$apks" >> "$GITHUB_OUTPUT"
       - name: Tar build dirs