[conformal/btcd] d6f7ad: Improve btcctl handling of empty RPC data returns.

[Dave Collins]

  Branch: refs/heads/master
  Home:   https://github.com/conformal/btcd
  Commit: d6f7adeba8ca027225759d2ba0da6660c5bfbfbe
      
https://github.com/conformal/btcd/commit/d6f7adeba8ca027225759d2ba0da6660c5bfbfbe
  Author: Dave Collins <da...@conformal.com>
  Date:   2014-05-13 (Tue, 13 May 2014)

  Changed paths:
    M util/btcctl/btcctl.go

  Log Message:
  -----------
  Improve btcctl handling of empty RPC data returns.

There are several RPCs which do not return any data on success.  btcctl
was improperly treating this as an error condition.