Fix MatrixVectorMultiply and incorrect DCHECKS.
Fix MatrixVectorMultiply and incorrect DCHECKS.

(Thanks to Serget Sharybin for reporting this)

Change-Id: I6bbc41667308fc2932871cf25ad07b431f70801f

entylop/ceres-solver,whuaegeanse/ceres-solver,timfel/ceres-bin,DougFirErickson/ceres-solver,entylop/ceres-solver,jmwalls/ceres-solver-fork,ysonggit/ceres-solver,kartikkumar/ceres-solver,ysonggit/ceres-solver,stonier/ceres_solver,timfel/ceres-bin,ikoruk/ceres-solver,kartikkumar/ceres-solver,DougFirErickson/ceres-solver,ikoruk/ceres-solver,kartikkumar/ceres-solver,DougFirErickson/ceres-solver,jmwalls/ceres-solver-fork,ikoruk/ceres-solver,DougFirErickson/ceres-solver,ysonggit/ceres-solver,ikoruk/ceres-solver,kartikkumar/ceres-solver,entylop/ceres-solver,ysonggit/ceres-solver,whuaegeanse/ceres-solver,ikoruk/ceres-solver,jmwalls/ceres-solver-fork,timfel/ceres-bin,entylop/ceres-solver,jmwalls/ceres-solver-fork,timfel/ceres-bin,stonier/ceres_solver,whuaegeanse/ceres-solver,stonier/ceres_solver,whuaegeanse/ceres-solver,stonier/ceres_solver