[histfactory] fix memory leak in HistoToWorkspaceFactory.cxx
[histfactory] fix memory leak in HistoToWorkspaceFactory.cxx

Forget to delete iterator. Also avoid crash when no POI found

olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root