Fixed ddd2isis so that it works with files that have headers with greater than...

Fixed ddd2isis so that it works with files that have headers with greater than 1024 bytes. Fixes #1594.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@5176 41f8697f-d340-4b68-9986-7bafba869bb8