Fix unbelievably broken code in put_vformat()

[Dirk Hohndel]

Dear hopped-up woodland creature...

On Sat, 2014-03-08 at 15:54 -0800, Linus Torvalds wrote:
> But no, the git object parsing code was fine, it was just my
> put_vformat() code that was utter crap, clearly written by some
> hopped-up woodland creature - me.
> 
> Christ, sometimes I wonder what bad drugs I'm on when writing code.
> And other times I wonder if I should perhaps be taking more, to forget
> the shame.

In case this helps you with your shame (and I doubt it)... I had read
through the broken code earlier this week as I was going trough the
Coverity reports on Subsurface. And even looked at the vsnprintf manpage
to make sure the length calculation was indeed correct.

And still didn't catch the problem.

Thanks for the patch.

Your fellow hopped up woodland creature

/D