Fix crasher when running 'ostree cat'

Cause was a buffer read overrun.

https://bugzilla.gnome.org/show_bug.cgi?id=705964

src/ostree/ot-builtin-cat.c

@@ -29,6 +29,7 @@
 #include <gio/gunixoutputstream.h>
 
 static GOptionEntry options[] = {
+  { NULL },
 };
 
 static gboolean