Backwards compatibility - class asset-align-right is ignored with imagecache formatter

I've updated to asset module 5.x-1.0-rc2 from 5.x-1.0-rc1
We use imagecache2 and lightbox2, and have a considerable amount of nodes, where images, set with asset module in tinyMCE, are displayed with attribute align right or left.
Actually the function theme_asset adds a class 'asset-align-right' to the image ...

Now, the new imagecache module 5.x-2.1 is adding a class as well in it's themeing function. So the asset-align-right simply is ignored by the browser ... and the image not aligned correctly.

I'm adding a patch to this issue, where the class is added if there is already a class in the image - or the whole class attribute is added to the image.

Hope this helps someone