Make sure quota_preset is using numerical indexes

If one set quota_present to "default, none, 1 GB, 5 GB, 10 GB" the old implementation will remove default and none but keep the array indexes. Later json_encode will recognize a array with 2 as first index as object and hence quotaPreset.reduce will fail.

Signed-off-by: Daniel Kesselberg <mail@danielkesselberg.de>