Fix 2 2 conflicts

Initially introduced in https://github.com/spree/spree-multi-domain/commit/167d40124c9167fc7fed4c5dee1bf73fd4145b03 with no tests, so it didn't blow up when `permalink` changed to `slug`.

I put quite a bit of effort into figuring out how to test it, but there's some before filter being introduced somewhere that sets @product before it gets here. I don't know why, but I have hit this in my app.

cc @JDutil