fix warning: type casting

git-svn-id: https://svn.mcs.anl.gov/repos/parallel-netcdf/trunk@1718 c368ceb8-fd28-0410-a457-e46ee1d7cd4a
fix warning: type casting

git-svn-id: https://svn.mcs.anl.gov/repos/parallel-netcdf/trunk@1719 c368ceb8-fd28-0410-a457-e46ee1d7cd4a