Another partial revert of r301289.

In this case, a change was made in one-true-awk from *FS to
getsval(fsloc) in a line just after one of the lines that had the 0 ->
NULL change. It works both ways as far as I can tell. It looks like a
bug fix, but I've not tried to track down which ancient version of
one-true-awk it was in (github starts too late for tracking this
down). Before and after the changes the regression suite is passes
100% relative to the un-modified one-true-awk.