Fix comparing array to null is always true
Fix comparing array to null is always true

This should be a strlen() comparison instead of comparing the
truthiness of an array.

This should be safe as everywhere does populate label, if only with
an empty string.

Signed-off-by: Stewart Smith <ec31ab75ddf977353c8f660f92ea8b23f64aef25@linux.vnet.ibm.com>

open-power/skiboot,qemu/skiboot,shenki/skiboot,csmart/skiboot,qemu/skiboot,shenki/skiboot,shenki/skiboot,csmart/skiboot,open-power/skiboot,shenki/skiboot,qemu/skiboot,legoater/skiboot,stewart-ibm/skiboot,stewart-ibm/skiboot,qemu/skiboot,open-power/skiboot,apopple/skiboot,legoater/skiboot,open-power/skiboot,open-power/skiboot,apopple/skiboot,legoater/skiboot,apopple/skiboot,csmart/skiboot,stewart-ibm/skiboot,legoater/skiboot,mikey/skiboot,qemu/skiboot,mikey/skiboot,shenki/skiboot,mikey/skiboot,legoater/skiboot