Category item Images are not Resized when Thumbnail and Fullsize are used

When I upload two versions of category item image (thumbnail and fullsize),
then they are not resized on the Front-End to match theme design. For now
images are only resized, when I upload one image in thumbnail field and
check "Same Images" checkbox. Because of this bug sites created before
auto-resize on demand functionality was developed (users were actually
uploading two image versions) are not able to auto-resize images to lower
site bandwidth.

I've created a patch, that should solve this problem, but I haven't tested
it for cases, where "Same Images" checkbox is checked and/or remote image
urls are specified. Please test mentioned cases.

After attached patch is applied all images, that are uploaded locally should
be able to auto-resize properly.