Polished the comments in src/core/index/ForwardIndex.cpp
Polished the comments in src/core/index/ForwardIndex.cpp

SRCH2/srch2-ngn,SRCH2/srch2-ngn,SRCH2/srch2-ngn,SRCH2/srch2-ngn,SRCH2/srch2-ngn,SRCH2/srch2-ngn,SRCH2/srch2-ngn