Fix problem in THcAerogel::CoarseProcess with fNpeSum

The line fNpeSum += fNegNpeSum
was basically double counting the fNegNpeSum
Same for fNpeSum += fPosNpeSum
since they were in a loop over Neg and Pos hits.

Just set
fNpeSum = fNegNpeSum + fPosNpeSum
after the two loops over Neg and Pos hits