ECM-8.1 encoding crash for SCC sequences when AMVR is off

The encoding crash may be reproduced with the following command line

./EncoderAppStatic -c ../cfg/encoder_randomaccess_ecm.cfg -c ../cfg/per-class/classF.cfg -i ../../../sequences/SlideShow_1280x720_20.y4m -dph 1 -f 9 -q 37 --IMV=0 --AffineAmvr=0

The encoding error message is

ERROR: In function "deriveBvdSignIBC" in /usr/local/google/home/xlxiangli/program/g-ecm/source/Lib/CommonLib/InterPrediction.cpp:19476: cMvdKnownAtDecoder.getHor() != 0