Fix AsyncIO reading seed queueing (#3940)

Fix AsyncIO reading seed queueing (#3940)

Fixes a bug in AsyncIO where we queue reads after opening a file so our queue will always be saturated (or as saturated as possible).
Previous code was looping up to `availableJobsCount` not realizing `availableJobsCount` was also decreasing in each iteration, so instead of queueing 10 jobs we'd queue 5 (and instead of 2 we'd queue 1).
This PR fixes the loop to queue as long as `availableJobsCount` is not 0.