[conformal/btcd] aea23d: Send nil when rescan is finished.

[Josh Rickmar]

  Branch: refs/heads/master
  Home:   https://github.com/conformal/btcd
  Commit: aea23ddff30c5a8a4fa4d25368488067e852b531
      
https://github.com/conformal/btcd/commit/aea23ddff30c5a8a4fa4d25368488067e852b531
  Author: Josh Rickmar <jr...@conformal.com>
  Date:   2013-12-02 (Mon, 02 Dec 2013)

  Changed paths:
    M rpcserver.go

  Log Message:
  -----------
  Send nil when rescan is finished.

I previously fixed the duplicate send (before seeing GH issue #54),
but forgot that btcwallet expects a nil reply when rescan has
finished.  This adds the final reply back, but replies with nil.

Fixes #54.