Bug fix: pass subpicture by reference instead of copying

source/Lib/CommonLib/AdaptiveLoopFilter.cpp

source/Lib/CommonLib/Mv.cpp

source/Lib/CommonLib/Slice.cpp

source/Lib/CommonLib/Slice.h

source/Lib/CommonLib/UnitTools.cpp

source/Lib/DecoderLib/DecLib.cpp

source/Lib/DecoderLib/DecSlice.cpp

source/Lib/EncoderLib/EncSlice.cpp

source/Lib/EncoderLib/InterSearch.cpp