Removed fatal error from CbmMCTrack if PDG code not found in TDatabasePDG. Refs #1826.
See Redmine issue 1826. In some places in simulations, non-standard PDF codes are defined and used. In such cases, CbmMCTrack cannot get mass and charge from TDatabasePDG. In the respective accessors, a fatal error was thrown, which is inconvenient. It is replaced by a LOG(error) in this MR.