The loop to generate seed data will exit on RAND_status(), so we don't
need to handle the case of RAND_poll() failing separately.  Failures
here are rare, so this a code cleanup, essentially.

Daniel Gustafsson, reviewed by David Steele and Michael Paquier.

Discussion: https://postgr.es/m/9B038FA5-23E8-40D0-B932-D515E1D8F66A@yesql.se