Bug 1986111

Description of problem:
When using groupdel with a prefix path, it segfaults on Fedora 34.
groupadd and groupmod both are working fine.

Version-Release number of selected component (if applicable):
shadow-utils-4.8.1-8.fc34.x86_64

How reproducible:
Every time groupdel is executed (as root)

Steps to Reproduce:
1. Create a custom /etc/group file, e.g. using
[root@fedora ~]# mkdir -p $HOME/custom_root/etc/ && touch $HOME/custom_root/etc/group
2. Create a group (succeeds)
[root@fedora ~]# groupadd -P $HOME/custom_root test_group
3. Delete the group (fails)
[root@fedora ~]# groupdel -P $HOME/custom_root test_group

Actual results:
[root@fedora ~]# groupdel -P $HOME/custom_root test_group
Segmentation fault (core dumped)

Expected results:
Return code 0 with the group deleted from $HOME/custom_root/etc/group

Additional info:
[root@fedora ~]# gdb --args groupdel -P $HOME/custom_root test_group
(gdb) run
Starting program: /usr/sbin/groupdel -P /root/custom_root test_group

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7df795b in fgetpos@@GLIBC_2.2.5 () from /lib64/libc.so.6
(gdb) bt
#0  0x00007ffff7df795b in fgetpos@@GLIBC_2.2.5 () from /lib64/libc.so.6
#1  0x00007ffff7e4d442 in fgetpwent () from /lib64/libc.so.6
#2  0x000055555555882c in main ()
(gdb) 

[root@fedora ~]# rpm -qa | grep glibc
glibc-all-langpacks-2.33-20.fc34.x86_64
glibc-common-2.33-20.fc34.x86_64
glibc-langpack-en-2.33-20.fc34.x86_64
glibc-2.33-20.fc34.x86_64
glibc-doc-2.33-20.fc34.noarch
glibc-headers-x86-2.33-20.fc34.noarch
glibc-devel-2.33-20.fc34.x86_64