Improve binary asset detection

`.otf` is a binary font file that isn't correctly detected by `ShopifyTheme.is_binary_data?`, so this Pull Request adds it to the binary extensions whitelist.

While I was there I noticed that the expensive `ShopifyTheme.is_binary_data?` method was always called regardless of the whitelist, so I figured it makes sense to swap the `if` conditions around so that the whitelist effectively guards that call too.