Remove invalid item id usage as media source id

Looking at the change history, it looks like an accidental ` || item.Id`
was introduced in 4c31742 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
c54db60 and
ca47635 for Live TV by not setting this
variable in that case.

src/components/playback/playbackmanager.js

@@ -2581,15 +2581,10 @@ export class PlaybackManager {
             }
 
             const apiClient = ServerConnections.getApiClient(item.ServerId);
-            let mediaSourceId;
-
+            const mediaSourceId = playOptions.mediaSourceId;
             const isLiveTv = [BaseItemKind.TvChannel, BaseItemKind.LiveTvChannel].includes(item.Type);
 
-            if (!isLiveTv) {
-                mediaSourceId = playOptions.mediaSourceId || item.Id;
-            }
-
-            const getMediaStreams = isLiveTv ? Promise.resolve([]) : apiClient.getItem(apiClient.getCurrentUserId(), mediaSourceId)
+            const getMediaStreams = isLiveTv ? Promise.resolve([]) : apiClient.getItem(apiClient.getCurrentUserId(), mediaSourceId || item.Id)
                 .then(fullItem => {
                     return fullItem.MediaStreams;
                 });