Improve ImageSetUpdater: more robust if jcr:data is not present; upscale per variant.

The standard image set updater script failed for a client because the property jcr:data was not present on the original image variant.

This was improved in the project by adding a session refresh like so

  } catch (RepositoryException e) {
    log.error("Failed in generating image variants", e);
    // added:        
    node.getSession().refresh(false);
  }

Let's put that in the standard script, and possibly also a hasProperty check before this piece of code:

  data.getProperty(JcrConstants.JCR_DATA).getBinary().getStream();