TStreamerInfo::Build: fix size calculation for synthetic TClass for pair.
TStreamerInfo::Build: fix size calculation for synthetic TClass for pair.

olifre/root,root-mirror/root,root-mirror/root,olifre/root,olifre/root,olifre/root,root-mirror/root,olifre/root,olifre/root,root-mirror/root,root-mirror/root,root-mirror/root,olifre/root,olifre/root,olifre/root,root-mirror/root,olifre/root,root-mirror/root,olifre/root,root-mirror/root,root-mirror/root,root-mirror/root