bugfix: protection for non-existing data source in CbmMCDataArray
Protection for non-existing data source in CbmMCDataArray.
The following code crashes when the "MvdPoint" branch is not present in the data:
CbmMCDataArray *points = CbmMCDataManager::InitBranch("MvdPoint"); // OK, points !=nullptr
points->Size(file, event); // crash
Edited by Sergey Gorbunov