Arvados

While working on 13933, I inadvertently reverted the concurrent map access bug that was fixed in 13788 (by moving the list var declaration out of the loop so that I could use it for the initial `limit: 0` `count: exact` call).

I would suggest adding a comment to the var declaration to make a particular point of it being absolutely necessary to declare it afresh in each loop iteration, as I suspect it would otherwise be likely that the same mistake will be made again.