static cast to force Eigen::Index to long conversion.
static cast to force Eigen::Index to long conversion.

Change-Id: I11945c455eb3fef9bfb952f5a30d657542fbccae

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