(bug 46787) API: Fix rccontinue handling

There are several bugs in Icc43b62f:
* When handing the continuation, the code checks for dir=descending when
  the actual value is dir=older.
* When the above is fixed, the continuation code assumes "ORDER BY
  rc_timestamp DESC, rc_id ASC", which would filesort.
* rc_id is not added to the ORDER BY clause anyway.

Bug: 46787
Change-Id: Ia6ebd4ea0458b8013d4ecb71954dcfbdacff2c00
Merge "(bug 46787) API: Fix rccontinue handling"