RingBuffer: Properly wait for readahead thread to start

Inverted test, no wait occurred causing a race condition later on which causes failures in LiveTV, usually when changing channels

(cherry picked from commit 6b29f598776f8a2ecba09674b4c900ce0fb1fe7f)
RingBuffer: always read directly from file if read ahead thread isn’t running

readInternalMode can only work if the read ahead thread is running

(cherry picked from commit 0641cd9ac3eb142f239b70085bac459f3694eadd)