(#22060) Fix undefined path in macaddress.rb

While running `puppet agent --no-daemonize --debug`, and IFF somewhere in the
code I have $DEBUG = true, then if I Ctrl-C to kill the agent I see the
following exception:

  Exception `NilClass' at .../facter/lib/facter/macaddress.rb:19 -
  undefined local variable or method `path' for :Facter::Util::Resolution

This is followed by an "infinite" recursion / stackoverflow.