At least one experimental NVMe card has passed through our test labs
that would interrupt before it was started and its completion queue
memory would read all 0's. This would lead us to believe we had a queue
size'd set of completions that completed w/o trackers. Work around this
by making sure we've submitted commands to queue when the cid tracker
lookup returns NULL. For cards w/o this issue, this code will never run.
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