### Summary

When using the user module to modify password_expire_min=0, the processing result does not meet expectations .
I guess the problem is caused by the following code in the user module.
```
    # deal with password expire min
    if user.password_expire_min:
        if user.user_exists():
            (rc, out, err) = user.set_password_expire_min()
```
Modifying to the following  code may fix this problem.
```
    # deal with password expire min
    if user.password_expire_min is not None:
        if user.user_exists():
            (rc, out, err) = user.set_password_expire_min()
```

### Issue Type

Bug Report

### Component Name

user

### Ansible Version

```console
$ ansible --version
ansible [core 2.11.1] 
  config file = None
  configured module search path = ['/home/betadmin/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /app/python3/lib/python3.8/site-packages/ansible
  ansible collection location = /home/betadmin/.ansible/collections:/usr/share/ansible/collections
  executable location = /app/python3/bin/ansible
  python version = 3.8.5 (default, Sep 18 2020, 14:55:53) [GCC 4.8.5 20150623 (Red Hat 4.8.5-16)]
  jinja version = 2.11.2
  libyaml = False
```


### Configuration

```console
$ ansible-config dump --only-changed
```


### OS / Environment

RHEL 7.4

### Steps to Reproduce

- name: Edit password_expire_min
  user:
    name: test
    password_expire_min: 0



### Expected Results

Minimum number of days between password change	: 0


### Actual Results


Minimum number of days between password change	: 2


### Code of Conduct

- [X] I agree to follow the Ansible Code of Conduct
cmd.append(self.ssh_bits)
        cmd.append('-C')
        cmd.append(self.ssh_comment)
        cmd.append('-f')
        cmd.append(ssh_key_file)
        if self.ssh_passphrase is not None:
            if self.module.check_mode:
                self.module.debug('In check mode, would have run: "%s"' % cmd)
                return (0, '', '')
            master_in_fd, slave_in_fd = pty.openpty()
            master_out_fd, slave_out_fd = pty.openpty()
            master_err_fd, slave_err_fd = pty.openpty()
            env = os.environ.copy()
            env['LC_ALL'] = get_best_parsable_locale(self.module)
            try:
                p = subprocess.Popen([to_bytes(c) for c in cmd],
                                     stdin=slave_in_fd,
                                     stdout=slave_out_fd,
                                     stderr=slave_err_fd,
                                     preexec_fn=os.setsid,
                                     env=env)
                out_buffer = b''
                err_buffer = b''
                while p.poll() is None:
                    r, w, e = select.select([master_out_fd, master_err_fd], [], [], 1)
                    first_prompt = b'Enter passphrase (empty for no passphrase):'
                    second_prompt = b'Enter same passphrase again'
                    prompt = first_prompt
                    for fd in r:
                        if fd == master_out_fd: