The callback that handles the initial sizing/scaling for images was sometimes running before jquery finished setting the `initial-width` and `initial-height` data, which could result in one of the two images in the two-up view being scaled and one not. This change adds a `_.defer` call to unwind the stack before we trigger that callback. Testing Done: Loaded a diff that had a bunch of changed images with @2x versions. Saw that I was no longer able to trigger the case where one out of the two images was full size and one was 50%.