Fix: Array bounds read in zprop_print_one_property()

If the loop index i comes to (ZFS_GET_NCOLS - 1), the cbp->cb_columns[i + 1]
actually read the data of cbp->cb_colwidths[0], which means the array
subscript is above array bounds.

Luckily the cbp->cb_colwidths[0] is always 0 and it seems we haven't
looped enough times to exceed the array bounds so far, but it's really
a secluded risk someday.

Signed-off-by: GeLiXin <ge.lixin@zte.com.cn>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #5003