Zero btree item padding as items are created

Item creation, which fills out a new item at the end of the array of
item structs at the start of the block, didn't explicitly zero the item
struct padding to 0.  It would only have been zero if the memory was
already zero, which is likely for new blocks, but isn't necessarily true
if the memory had previously been used by deleted values.

Signed-off-by: Zach Brown <zab@versity.com>

kmod/src/btree.c

@@ -521,6 +521,7 @@ static void create_item(struct scoutfs_btree_block *bt,
 
 	item->val_off = insert_value(bt, ptr_off(bt, item), val, val_len);
 	item->val_len = cpu_to_le16(val_len);
+	memset(item->__pad, 0, sizeof(item->__pad));
 
 	le16_add_cpu(&bt->total_item_bytes, item_bytes(item));
 }