The "right" way to fix that bathtub-door problem, I suspect, would be to have someone recut (and re-frame) the sliding door so that it, itself, is not square, but instead matches the non-squareness of the wall.

Either that, or one could shim the jamb out from the wall so that it was perpendicular to the rails. Doing that in a way that didn't look shoddy would probably be a bit of a trick, though.