[BUG REPORT] Git log pretty date

Hi,

I'm having some problems with the `git log` command.

Setup: Happens in multiple versions, tested on 1.8.* and 2.*

The problem happens when I try to get a pretty log for a commit with a wrong date.

Executing the command: `git log --encoding=UTF-8 --date=raw --pretty=format:'%H,%P,%ad,%cd,%an,%s'`

I get an empty response on the date field, but since pretty has `%ad` it should follow the --date and return the date even if wrong.

The problem happens in this repo: `https://github.com/SamWM/jQuery-Plugins` on commit `e9dddaf24c9de45d9b4efdf38eff7c30eb200f48`.

I posted it on SO too: `http://stackoverflow.com/questions/23793188/find-date-for-not-dated-commit`

I think it is a bug probably on pretty since other raw formats show the date as it should.

I tried to check the source code but have no idea where to start, maybe if you point me on some direction I can take a look for my self.

Can you help?

Kind regards, Rodrigo Fernandes