osd/PrimaryLogPG: avoid dereferencing invalid complete_to

osd/PrimaryLogPG: avoid dereferencing invalid complete_to

For the auto-repair (EIO caused) case, we will not reinitialize
**complete_to** (because last_complete is equal to last_update!)
and hence there is chance that **complete_to** should aleady
point to **log.end()** before we call recover_got.

We could simply drop it here as we (already) logged the **complete_to**
iterator change in a more compatible way a few lines below.

Signed-off-by: xie xingguo <xie.xingguo@zte.com.cn>
(cherry picked from commit 69a2cc35840939436da09691ca62476d7f599de4)