[Libburn] patch libisofs/tree.c to avoid null pointer reference

[Derek Foreman]

On Fri, 27 Aug 2004, Alan Jenkins wrote:

> Hopefully the attached patch should be self explanatory.  I think you would 
> always get a null pointer ref if the directory name was invalid.  I will 
> check the function  for adding a file as well

The patch looks good to me.  I'll merge it sometime this weekend if Todd 
or Benji don't sound off against it.

Thanks