htab_delete(): fix failure to set tombstone

we can't just set an item's key to zero and be done with a deletion,
because this will break the item search chain.
a deleted item requires a special marker, also known as tombstone.
when searching for an item, all slots with a tombstone need to treated
as if they were in use, but when inserting an item such a slot needs
to be filled with the new item.

a common procedure is to rehash the table when the number of deleted
items crosses a certain threshold, though for simplicity we leave this
task to the resize() function which does the same thing anyway when
the hashtable grows.

this allows to fix the issue quite elegantly and with almost no
additional overhead, so we don't penalize applications that do very
few deletions.

0 files changed, 0 insertions, 0 deletions