Tiny changes to prevent a signed/unsigned compile warning.
Tiny changes to prevent a signed/unsigned compile warning.

Change-Id: Id80bad85009df7be039324609528c944b3195c60

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