Fix SegmentSelector::empty() on double-fault post (#305)
Fix SegmentSelector::empty() on double-fault post (#305)

The “Double Fault“ post still use the old `SegmentSelector::empty()` on
the x86 crate. This commit update it to the new x86_64 crate.
phil-opp/blog_os,phil-opp/blog_os,phil-opp/blogOS,phil-opp/blogOS,phil-opp/blog_os,phil-opp/blog_os