This closes#9495. As detailed in there, the collection query GET
/v1/volumes?type=csi doesn’t return ReadAllocs and WriteAllocs, so the #
Allocs cell was always showing 0 upon first load because it was derived
from the lengths of those arrays. This uses the heretofore-ignored
CurrentReaders and CurrentWriters values to calculate the total instead.
The single-resource query GET /v1/volume/csi%2F:id doesn’t return
CurrentReaders and CurrentWriters that absence doesn’t override the
stored values when visiting an individual item.
Thanks to @apollo13 for reporting this and to @tgross for the API logs
and suggestion.