queue2: avoid waiting for a filled buffer

queue2: avoid waiting for a filled buffer

Use a threshold variable to hold the maximum distance from the current position
for with we will wait instead of doing a seek.
When using the ringbuffer and the requested offset is not available, avoid
waiting until the complete ringbuffer is filled but instead do a seek when the
requested data is further than the threshold.
Avoid doing the seek twice in the ringbuffer case.
Use the same threshold for ringbuffer and download buffering.