a simpler way to determine if we need to free up cbuf

git-svn-id: https://svn.mcs.anl.gov/repos/parallel-netcdf/trunk@1785 c368ceb8-fd28-0410-a457-e46ee1d7cd4a
check expected error code if starts is NULL

git-svn-id: https://svn.mcs.anl.gov/repos/parallel-netcdf/trunk@1786 c368ceb8-fd28-0410-a457-e46ee1d7cd4a