[cmyth] Improve global speed of live TV playback (read and seek)

Hold handled chain and file and not dereference any more. Now client doesn't need to hold a mutex because handled resources will never freed during operations. Also It is possible because none of volatile values are critical in the context of these operations.
No need to hold recorder because all called sub functions handle null recorder and we bail out.
[mythtv-cmyth] Improve global speed of live TV playback (read and seek)

Relates cmyth changes. Now client doesn't need to hold a mutex because handled resources will never freed during operations.