CxxUtils: Suppress an ubsan warning originating from ROOT.
Suppress warning /cvmfs/sft.cern.ch/lcg/releases/gcc/8.3.0.1-0a5ad/x86_64-centos7/include/c++/8.3.0/bits/stl_iterator.h:797:17: runtime error: reference binding to null pointer of type 'unsigned int' caused in TStreamerInfoActions::VectorLooper::ReadCollectionBasicType when reading an empty vector: T *begin = &(*vec->begin()); buf.ReadFastArray(begin, nvalues);