[Backport r51221 | neal.norwitz -- the original commit message is wrong;

[Backport r51221 | neal.norwitz -- the original commit message is wrong;
 this code is only used if WITHOUT_COMPLEX is *not* defined, which is the
 common case for Python builds.]

This code is actually not used unless WITHOUT_COMPLEX is defined.
However, there was no error checking that PyFloat_FromDouble returned
a valid pointer.  I believe this change is correct as it seemed
to follow other code in the area.

Klocwork # 292.