submodules in diff

repository.blob_at also find submodules
related to https://github.com/gitlabhq/gitlabhq/pull/7389 
I don't know it's a bug in grit. a_mode is nil in grit that's way I can't hide "View file" button here https://cloud.githubusercontent.com/assets/1488195/3720833/2900e428-165a-11e4-9826-5687e44d8b1d.png.
I'm not sure that it's possible to fix now.