fix a bug in cncom.h & speed up AddVMerged(const TVec&)#224

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zhaolu996 wants to merge 2 commits intosnap-stanford:masterfrom zhaolu996:master

+17-2

Commits on Jul 5, 2021

improve the efficiency of AddVMerged(const TVec<TVal>&) in snap-core/ds.h. (tested)
zhaolu996
committed
fix bug in IsNIdIn(const TInt&) in snap-core/cncom.h; test codes are added.
zhaolu996
committed