fix decoder crash under CTC for subpicture

...onCTC-SliceConfigExamples/subpicture_4Slice2HorSubPic.cfg

...onCTC-SliceConfigExamples/subpicture_4Slice2VerSubPic.cfg

source/App/DecoderApp/DecApp.cpp

source/App/DecoderApp/DecAppCfg.cpp

source/App/DecoderApp/DecAppCfg.h

source/Lib/CommonLib/Slice.cpp

source/Lib/CommonLib/Slice.h

source/Lib/CommonLib/TypeDef.h

source/Lib/DecoderLib/DecLib.cpp

source/Lib/DecoderLib/DecLib.h

source/Lib/DecoderLib/DecSlice.cpp

source/Lib/DecoderLib/VLCReader.cpp

source/Lib/EncoderLib/EncSlice.cpp