traverse: Set an explicit error when loading a corrupted commit
traverse: Set an explicit error when loading a corrupted commit

I had a empty files for a .commit and .dirmeta, and previously we were
segfaulting.

gatispaeglis/ostree,GNOME/ostree,leandrosansilva/ostree,GNOME/ostree,gatispaeglis/ostree,gatispaeglis/ostree,resin-io/ostree,sujitfulse/ostree,sujitfulse/ostree,leandrosansilva/ostree,resin-io/ostree,sujitfulse/ostree,resin-io/ostree,sujitfulse/ostree,sujitfulse/ostree,GNOME/ostree,GNOME/ostree,GNOME/ostree,leandrosansilva/ostree,gatispaeglis/ostree,resin-io/ostree,gatispaeglis/ostree,leandrosansilva/ostree,leandrosansilva/ostree,gatispaeglis/ostree,resin-io/ostree