[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.
[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.