circular_buffer: do not destroy uninitialized object
circular_buffer: do not destroy uninitialized object

If an object creation fails during copying with an exception do not call
destructor of an object whose creation was not complete.

sjperkins/seastar,hongliangzhao/seastar,stamhe/seastar,leejir/seastar,acbellini/seastar,bowlofstew/seastar,norcimo5/seastar,tempbottle/seastar,joerg84/seastar,syuu1228/seastar,scylladb/seastar,jonathanleang/seastar,linearregression/seastar,jonathanleang/seastar,acbellini/seastar,avikivity/seastar,scylladb/scylla-seastar,koolhazz/seastar,printedheart/seastar,wildinto/seastar,kjniemi/seastar,scylladb/seastar,hongliangzhao/seastar,xtao/seastar,shyamalschandra/seastar,flashbuckets/seastar,xtao/seastar,avikivity/seastar,wildinto/seastar,tempbottle/seastar,acbellini/seastar,linearregression/seastar,shyamalschandra/seastar,cloudius-systems/seastar,bowlofstew/seastar,dreamsxin/seastar,syuu1228/seastar,flashbuckets/seastar,stamhe/seastar,koolhazz/seastar,wildinto/seastar,syuu1228/seastar,hongliangzhao/seastar,koolhazz/seastar,stamhe/seastar,chunshengster/seastar,anzihenry/seastar,anzihenry/seastar,anzihenry/seastar,flashbuckets/seastar,shyamalschandra/seastar,kjniemi/seastar,avikivity/seastar,scylladb/scylla-seastar,cloudius-systems/seastar,scylladb/seastar,bowlofstew/seastar,joerg84/seastar,tempbottle/seastar,jonathanleang/seastar,leejir/seastar,scylladb/scylla-seastar,sjperkins/seastar,kjniemi/seastar,dwdm/seastar,chunshengster/seastar,dwdm/seastar,norcimo5/seastar,leejir/seastar,joerg84/seastar,printedheart/seastar,dwdm/seastar,printedheart/seastar,dreamsxin/seastar,norcimo5/seastar,chunshengster/seastar,xtao/seastar,dreamsxin/seastar,cloudius-systems/seastar,sjperkins/seastar,linearregression/seastar