Before this change, sgetsgent_r did not set errno to ERANGE, but
sgetsgent only check errno, not the return value from sgetsgent_r.
Consequently, sgetsgent did not detect any error, and reported
success to the caller, without initializing the struct sgrp object
whose address was returned.
This commit changes sgetsgent_r to set errno as well. This avoids
similar issues in applications which only change errno.
Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
