sstables: improve check_truncate_and_assign()
sstables: improve check_truncate_and_assign()

 +    if (from >= std::numeric_limits<T>::max()) {
Avi explains an issue with the snippet above from the function:
This misses the case where either type is signed. At best you'd
get a compiler warning about comparing types with different
signedness, at worst a negative value can be truncated.

Signed-off-by: Raphael S. Carvalho <1e2942cea40e3b4d2162dfcd9e53e41c05a84d22@cloudius-systems.com>

glommer/scylla,linearregression/scylla,wildinto/scylla,asias/scylla,glommer/scylla,capturePointer/scylla,phonkee/scylla,stamhe/scylla,phonkee/scylla,duarten/scylla,wildinto/scylla,justintung/scylla,acbellini/scylla,acbellini/scylla,avikivity/scylla,rentongzhang/scylla,tempbottle/scylla,scylladb/scylla,gwicke/scylla,kjniemi/scylla,bowlofstew/scylla,kjniemi/scylla,acbellini/scylla,victorbriz/scylla,respu/scylla,kangkot/scylla,eklitzke/scylla,rluta/scylla,respu/scylla,stamhe/scylla,victorbriz/scylla,gwicke/scylla,aruanruan/scylla,phonkee/scylla,dwdm/scylla,bowlofstew/scylla,duarten/scylla,scylladb/scylla,scylladb/scylla,rentongzhang/scylla,shaunstanislaus/scylla,tempbottle/scylla,capturePointer/scylla,eklitzke/scylla,rentongzhang/scylla,asias/scylla,victorbriz/scylla,dwdm/scylla,senseb/scylla,kangkot/scylla,wildinto/scylla,respu/scylla,guiquanz/scylla,kjniemi/scylla,raphaelsc/scylla,stamhe/scylla,gwicke/scylla,eklitzke/scylla,guiquanz/scylla,senseb/scylla,aruanruan/scylla,glommer/scylla,guiquanz/scylla,linearregression/scylla,justintung/scylla,linearregression/scylla,capturePointer/scylla,scylladb/scylla,aruanruan/scylla,dwdm/scylla,bowlofstew/scylla,raphaelsc/scylla,tempbottle/scylla,shaunstanislaus/scylla,senseb/scylla,raphaelsc/scylla,rluta/scylla,rluta/scylla,avikivity/scylla,avikivity/scylla,asias/scylla,kangkot/scylla,duarten/scylla,shaunstanislaus/scylla,justintung/scylla