Item ID is used as MediaSourceId

[Kevinjil]

Describe The Bug
I am debugging playback issues of my plugin implementing the IChannel interface and I noticed that the call sent to the /Items/<uid>/PlaybackInfo now contains a key MediaSourceId in the JSON, which equals the uid of the URL. With this key set, the JF server returns no compatible streams. When fetching from the 10.9 webclient (with a JF 10.10 server), this key is missing and the server does report streams and playback starts.

Looking at the JF source, there is some filtering if this key is set. It appears that this key should not be set to the item.Id value.

Looking at the change history, it looks like an accidental || item.Id was introduced in #6112 to query for the item, perhaps not realising it is later used in the query later on for server-side filtering. This was partially fixed by #6166 for Live TV by not setting this variable in that case.

Media Information
N/A

Screenshots
N/A

System (please complete the following information):

• Platform: Linux
• Browser: Firefox
• Jellyfin Version: 10.10.3

Additional Context
N/A