### Please describe the problem.

git-annex throws an error message (see below) when trying to add a file whose name includes a space.


### What version of git-annex are you using? On what operating system?

git-annex version: 6.20161012
build flags: ConcurrentOutput Feeds Quvi
uname -srm: Linux 4.7.10-hardened x86_64


### Please provide any additional information below.

[[!format sh """
aranea@gentp ~/t/annex-test $ git init .
Initialized empty Git repository in /home/aranea/tmp/annex-test/.git/
aranea@gentp ~/t/annex-test master $ git annex init
init  ok
(recording state in git...)
aranea@gentp ~/t/annex-test master $ touch 'foo bar'
aranea@gentp ~/t/annex-test master $ git annex add
add foo bar git-annex: unknown response from git cat-file ("HEAD:./foo bar missing",Ref "HEAD:./foo bar")
CallStack (from HasCallStack):
  error, called at ./Git/CatFile.hs:102:28 in main:Git.CatFile
"""]]

> What an embarrasing reversion. [[fixed|done]] and I'll push a release for
> it right away. --[[Joey]]