When copying or moving between two local storages the source path (on
disk) to copy or move from is got from the unjailed path of the source
storage. However, if the source storage has more than one jail getting
the unjailed path resolves the most external jail, but the source path
needs to be got from the most internal jail instead (the one closer to
the local storage).

This can happen, for example, with a shared groupfolder: in that case
there is an external jail for the shared storage, and one internal jail
for the groupfolder storage wrapped by the shared storage.

Signed-off-by: Daniel Calviño Sánchez <[email protected]>