- POSIX prohibits printing errors to stderr here and require
returning NULL:
"Upon successful completion, initstate() and setstate() shall return a
pointer to the previous state array; otherwise, a null pointer shall
be returned.
Although some implementations of random() have written messages to
standard error, such implementations do not conform to POSIX.1-2008."
- Move error detections earlier to prevent state modifying.
MFC after: 1 week