tests: fix fstream_test use-after-free
tests: fix fstream_test use-after-free

guiquanz/scylla,dwdm/scylla,acbellini/scylla,flashbuckets/seastar,syuu1228/seastar,victorbriz/scylla,norcimo5/seastar,scylladb/scylla,senseb/scylla,koolhazz/seastar,scylladb/seastar,shaunstanislaus/scylla,hongliangzhao/seastar,xtao/seastar,kjniemi/scylla,linearregression/seastar,leejir/seastar,printedheart/seastar,sjperkins/seastar,hongliangzhao/seastar,duarten/scylla,shyamalschandra/seastar,avikivity/scylla,dreamsxin/seastar,gwicke/scylla,glommer/scylla,aruanruan/scylla,kangkot/scylla,duarten/scylla,shyamalschandra/seastar,chunshengster/seastar,xtao/seastar,printedheart/seastar,linearregression/seastar,gwicke/scylla,phonkee/scylla,syuu1228/seastar,wildinto/seastar,joerg84/seastar,anzihenry/seastar,norcimo5/seastar,capturePointer/scylla,avikivity/seastar,phonkee/scylla,scylladb/scylla,aruanruan/scylla,kjniemi/scylla,anzihenry/seastar,linearregression/scylla,tempbottle/scylla,joerg84/seastar,capturePointer/scylla,linearregression/scylla,kjniemi/seastar,shaunstanislaus/scylla,stamhe/scylla,dwdm/scylla,scylladb/scylla-seastar,rluta/scylla,dwdm/seastar,kjniemi/scylla,eklitzke/scylla,raphaelsc/scylla,flashbuckets/seastar,guiquanz/scylla,bowlofstew/seastar,senseb/scylla,kjniemi/seastar,tempbottle/scylla,scylladb/scylla,shyamalschandra/seastar,stamhe/seastar,stamhe/scylla,acbellini/scylla,cloudius-systems/seastar,linearregression/seastar,acbellini/seastar,justintung/scylla,scylladb/scylla,eklitzke/scylla,rentongzhang/scylla,leejir/seastar,leejir/seastar,justintung/scylla,bowlofstew/seastar,anzihenry/seastar,avikivity/scylla,eklitzke/scylla,scylladb/scylla-seastar,koolhazz/seastar,printedheart/seastar,rentongzhang/scylla,duarten/scylla,dreamsxin/seastar,bzero/seastar,respu/scylla,stamhe/scylla,asias/scylla,rentongzhang/scylla,cloudius-systems/seastar,joerg84/seastar,victorbriz/scylla,avikivity/seastar,justintung/scylla,aruanruan/scylla,kjniemi/seastar,stamhe/seastar,asias/scylla,wildinto/scylla,acbellini/seastar,jonathanleang/seastar,bowlofstew/seastar,cloudius-systems/seastar,bowlofstew/scylla,koolhazz/seastar,tempbottle/seastar,rluta/scylla,capturePointer/scylla,rluta/scylla,scylladb/scylla-seastar,glommer/scylla,hongliangzhao/seastar,senseb/scylla,xtao/seastar,jonathanleang/seastar,bowlofstew/scylla,bowlofstew/scylla,scylladb/seastar,gwicke/scylla,tempbottle/seastar,avikivity/scylla,flashbuckets/seastar,raphaelsc/scylla,wildinto/seastar,victorbriz/scylla,mixja/seastar,stamhe/seastar,linearregression/scylla,respu/scylla,dwdm/seastar,asias/scylla,syuu1228/seastar,phonkee/scylla,tempbottle/seastar,sjperkins/seastar,glommer/scylla,chunshengster/seastar,guiquanz/scylla,scylladb/seastar,wildinto/scylla,acbellini/scylla,respu/scylla,acbellini/seastar,dwdm/seastar,norcimo5/seastar,shaunstanislaus/scylla,raphaelsc/scylla,kangkot/scylla,mixja/seastar,jonathanleang/seastar,mixja/seastar,tempbottle/scylla,wildinto/scylla,avikivity/seastar,dwdm/scylla,bzero/seastar,sjperkins/seastar,bzero/seastar,dreamsxin/seastar,chunshengster/seastar,wildinto/seastar,kangkot/scylla