libpwdgrp: code shrink

libpwdgrp: code shrink

function                                             old     new   delta
parse_common                                         206     205      -1
getgrouplist_internal                                229     225      -4
bb_internal_getpwent_r                               182     173      -9
getXXnam                                             232     222     -10
getXXnam_r                                           216     176     -40
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(add/remove: 0/0 grow/shrink: 0/5 up/down: 0/-64)             Total: -64 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>