Use nullptr instead of NULL

source/App/DecoderApp/DecApp.cpp

source/App/EncoderApp/EncAppCfg.cpp

source/App/Parcat/parcat.cpp

source/App/SEIRemovalApp/SEIRemovalApp.cpp

source/App/SubpicMergeApp/SubpicMergeApp.cpp

source/Lib/CommonLib/AdaptiveLoopFilter.cpp

source/Lib/CommonLib/Buffer.h

source/Lib/CommonLib/CommonDef.h

source/Lib/CommonLib/DeblockingFilter.cpp

source/Lib/CommonLib/Hash.cpp

source/Lib/CommonLib/IbcHashMap.cpp

source/Lib/CommonLib/InterPrediction.cpp

source/Lib/CommonLib/InterPrediction.h

source/Lib/CommonLib/IntraPrediction.cpp

source/Lib/CommonLib/ParameterSetManager.h

source/Lib/CommonLib/Picture.cpp

source/Lib/CommonLib/RdCost.h

source/Lib/CommonLib/Rom.cpp

source/Lib/CommonLib/SEIColourTransform.cpp

source/Lib/CommonLib/SEIFilmGrainSynthesizer.cpp