[CBRD-24555] The spage_collect_statistics function should consider re…

…cords deleted by vacuum when calculating the number of records in a data page (#3944)

http://jira.cubrid.org/browse/CBRD-24555

Description

handled the requirements not to count vacuumed records in the spage_collect_statistics function
however, vacuumed records are not already being counted
// spage_vacuum_slot()
slot_p->offset_to_record = SPAGE_EMPTY_OFFSET;

// spage_collect_statistics()
if (slot_p->offset_to_record == SPAGE_EMPTY_OFFSET)
  {
    continue;
  }
but, I modified it for the following reasons
more intuitive to use slot_p->record_type instead of slot_p->offset_to_record in the spage_collect_statistics function
the spage_mark_deleted_slot_as_reusable function does not set slot_p->offset_to_record to SPAGE_EMPTY_OFFSET
defensive code by quick fix - leave 'if (slot_p->offset_to_record == SPAGE_EMPTY_OFFSET)' as it is

src/storage/slotted_page.c

@@ -1033,6 +1033,8 @@ spage_collect_statistics (PAGE_PTR page_p, int *npages, int *nrecords, int *rec_
     {
       if (slot_p->offset_to_record == SPAGE_EMPTY_OFFSET)
 	{
+	  assert (slot_p->record_type == REC_MARKDELETED || slot_p->record_type == REC_DELETED_WILL_REUSE);
+
 	  continue;
 	}