ReplicatedPG::make_writeable: check for evicted clone before adjusting for clone_overlap

Fixes: #7964
Signed-off-by: Samuel Just <sam.just@inktank.com>
ReplicatedPG::trim_object: account evicted prev clone for stats

If the previous clone is evicted, we shouldn't adjust the stats to
account for its new clone_overlap value.

Fixes: #7964
Signed-off-by: Samuel Just <sam.just@inktank.com>