posixfs scan fails to assimilate new files in disabled spaces

The assimilation of new files in disabled spaces triggered by a scan fails because an internal call to [readNode](https://github.com/opencloud-eu/reva/blob/main/pkg/storage/pkg/decomposedfs/node/node.go#L458) fails because it disregards disabled spaces.

This needs to be fixed so that new files in disabled spaces are picked up properly as well.