fix varm API when stride == NULL and imap != NULL fix bug when NC_check_id() failed, nc should not be used.
fix varm API when stride == NULL and imap != NULL
fix bug when NC_check_id() failed, nc should not be used.

Unidata/netcdf-c,Unidata/netcdf-c,Unidata/netcdf-c,Unidata/netcdf-c