storage: always fetch the redirect object for the requested prefix
storage: always fetch the redirect object for the requested prefix

The list command for a some "prefix/" will not get the associated
"prefix" HTML redirect object if it exists. This leads the indexing code
to assume it doesn't exist and always rewrites it. Avoiding extra writes
by making extra gets seems like a fair trade.

dm0-/mantle,glevand/coreos--mantle,quantum/coreos-mantle,glevand/coreos--mantle,mjg59/mantle,mjg59/mantle,marineam/mantle,marineam/mantle,dm0-/mantle,quantum/coreos-mantle