[master] fix false positive compiler warning
[master] fix false positive compiler warning

a "pointer always evaluates to true" warning was blocking
compilation of the radix ATF test when using --enable-developer
with gcc 4.8.2.

each/bind9-collab,pecharmin/bind9,each/bind9-collab,each/bind9-collab,pecharmin/bind9,pecharmin/bind9,each/bind9-collab,pecharmin/bind9,pecharmin/bind9,each/bind9-collab,each/bind9-collab,pecharmin/bind9