osd/OSDMap: do not trust partially simplified pg_upmap_item

osd/OSDMap: do not trust partially simplified pg_upmap_item

If we simplified a partially no-op pg_upmap_item, we shall still
continue to verify that the remaining part is valid.
The bug is introduced by 02e5499b350bcd7d9eac98b2072052a9a4a1f535,
before which we always validate the correctness of a pg_upmap_item
before trying to cancel or simplify it.

Fixes: https://tracker.ceph.com/issues/42052
Signed-off-by: xie xingguo <xie.xingguo@zte.com.cn>
(cherry picked from commit 4196b13283144de966eeba40e6765f10b254dac6)