git-completion.zsh does not escape spaces in filenames

Hi,

git-completion.zsh does not seem to properly escape spaces in filenames.

My git version: 2.9.2
My zsh version: 5.0.8

Expected behaviour: When completing filenames that contain spaces, for
example "foo bar", I would expect the git completion to complete "git
add foo<TAB>" to "git add foo\ bar".

Actual behaviour:

touch "foo bar"
git add foo<TAB>

results in:
git add foo bar

I am not a zsh expert, but apparently the usage of "compadd -Q" in
contrib/complete/git-completion.zsh prevents zsh from escaping spaces.

Is this behaviour intentional, or is this a bug?

Best,
Sebastian