[JSON-RPC] FIX: Do not reopen PVR playback when new channel requested

I changed the behavior of the JSON-RPC PlayerOperations, to not reopen the whole PVR playback, when a client requests a channel-id to be played and PVR playback is already active.
Not a big contribution, but this makes channel changes from JSON-RPC clients a lot faster.

I'd consider this to be a fix or small improvement. At least this time I'm not messing with the API and would appreciate if this made its way into Helix.