[cmyth] Fix access of freed memory in cmyth_livetv_chain_setup

Invalid read of size 2
  at 0x53A673: cmyth_livetv_chain_setup (livetv.c:723)
  by 0x53B73E: cmyth_spawn_live_tv (livetv.c:1318)
  by 0x510EF2: MythRecorder::SpawnLiveTV(MythChannel&) (MythRecorder.cpp:162)
  by 0x4E9F3C: PVRClientMythTV::OpenLiveStream(PVR_CHANNEL const&) (pvrclient-mythtv.cpp:1455)