Patch for tying stock level to option images

The node object currently loads option images in an array even if the option does not have any stock. I looked at how adjustments are managed and created a patch for uc_option_image.module to look at the stock level of an option and only provide those with a positive stock level (as appropriate) to the node object.

The attached patch also incorporates the fix for the image browse and preview options not showing up (!empty($file) from a previous fix).

Hopefully the stock tie-in is useful to someone.