fix possible segmentation fault

alib2common/src/XmlApi.hpp

alib2common/src/exception/CommonException.cpp

alib2common/src/exception/CommonException.h

alib2common/src/object/Object.cpp

alib2common/src/object/Object.h

alib2common/src/object/Void.cpp

alib2common/src/object/Void.h

alib2data/src/alphabet/BarSymbol.cpp

alib2data/src/alphabet/BarSymbol.h

alib2data/src/alphabet/BlankSymbol.cpp

alib2data/src/alphabet/BlankSymbol.h

alib2data/src/alphabet/BottomOfTheStackSymbol.cpp

alib2data/src/alphabet/BottomOfTheStackSymbol.h

alib2data/src/alphabet/EndSymbol.cpp

alib2data/src/alphabet/EndSymbol.h

alib2data/src/alphabet/LabeledSymbol.cpp

alib2data/src/alphabet/LabeledSymbol.h

alib2data/src/alphabet/NonlinearVariableSymbol.cpp

alib2data/src/alphabet/NonlinearVariableSymbol.h

alib2data/src/alphabet/RankedSymbol.cpp