Reapply r301691:

Revert r301689 - one-true-awk: Avoid a NULL dereference.

I got this wrong and the coverity report doesn't match the NetBSD change,
which was thought for a different version.

The change wouldn't hurt but let's wait until upstream figures this out.

(cherry picked from commit 2675e1b91dcfa744a414a42f5522f4fed958476c)