Running `zfs list -o avail rpool` resulted in a core dump.
This commit will fix this.
Run the needed overhead only, when `use_color()` is true.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: George Wilson <gwilson@delphix.com>
Signed-off-by: Tino Reichardt <milky-zfs@mcmilk.de>
Closes#14712