Fix for "auto-generated images appear as black" bug

[Eric McDonald]

Hi Matthew,

mskala@ansuz.sooke.bc.ca wrote:

> Anyway, there are a few lines that have to be re-arranged to fix it, and
> this patch does that.  Other bugs are made more visible by this patch (in
> particular, the "choose one subimage at random" code doesn't work with
> shrunken or magnified images), and *really* shrunken images (like, down to
> a single pixel as used at very low magnificatons) don't happen because of
> hardcoded limits elsewhere, but at least it's an improvement.

Yes, it is definitely an improvement.

Patch read, understood, applied, tested, and committed.

   Thanks,
      Eric