Now that you can specify negative indents in Halibut text mode, it's

possible to specify an indent which is _overall_ negative, i.e.
intended to be off the left-hand side of the text file. There's no
nice way to handle this, but printing O(2^32) spaces in a while (n--)
loop is particularly bad. Fix the loop to read while (n-- > 0), so
that at least it doesn't get _that_ badly confused.

git-svn-id: svn://svn.tartarus.org/sgt/halibut@9491 cda61777-01e9-0310-a592-d414129be87e