Disconnection or logout can leave pending requests and channels

[noahwilliamsson]

When we're disconnected (because of errors or because of logout) there might be several requests that are in a pending state.

• Login might be processed
• Playlists might be retrieved
• Tracks/artists/albums metadata might be retrieved

These requests should either be aborted (if in REQ_STATE_RUNNING) or postponed (in REQ_STATE_NEW).

Otherwise corruption or NULL pointer dereferences might occur due to sp_session::login or sp_session::playlist_ctx being stale