client restore: don't add server file ending if already specified

client restore: don't add server file ending if already specified

If one executes a client command like
 # proxmox-backup-client files <snapshot> --repository ...
the files shown have already the '.fidx' or '.blob' file ending, so
if a user would just copy paste that one the client would always add
.blob, and the server would not find that file.

So avoid adding file endings if it is already a known OK one.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>