[IoContext] Add missing error handling in submitPreparedSqesAndWait()

Within the

do { reapAndScheduleCompletions() } while (io_uring_submit() == -EBUSY)

loop, the return value of io_uring_submit could be a negative value other than EBUSY. In that case, we did not DIE.

Looking at the SubmitActor, where we have a very similar loop, the error handling is correct. This changes the error handling in IoContext to match the one of SubmitActor, even though it has a little bit more overhead.