Set the max open file value to the current limit if setrlimit() fails

In set_max_file_descriptors(), if setrlimit() fails, we log warn and bail out leaving the max_out pointer unset.

It should be set to the current value returned by getrlimit() before we try to change it with setrlimit().

Flagging this as critical because right now on commit e48f8e5e, if the ed25519_master_id_public_key can't be opened, tor shuts down.