[pgsql] fix usage of sizeof operator in SetString
[pgsql] fix usage of sizeof operator in SetString

It does not return size of allocated memory,
therefore just reallocate buffer if maxsize bigger than standard buffer
olifre/root,root-mirror/root,olifre/root,root-mirror/root,olifre/root,root-mirror/root,root-mirror/root,root-mirror/root,olifre/root,root-mirror/root,root-mirror/root,olifre/root,olifre/root,olifre/root,root-mirror/root,root-mirror/root,olifre/root,root-mirror/root,root-mirror/root,olifre/root,olifre/root,olifre/root