### 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
test1:
                password = *
                lastupdate = 1553695126
        """
        b_name = to_bytes(self.name)
        b_passwd = b''
        b_expires = b''
        if os.path.exists(self.SHADOWFILE) and os.access(self.SHADOWFILE, os.R_OK):
            with open(self.SHADOWFILE, 'rb') as bf:
                b_lines = bf.readlines()
            b_passwd_line = b''
            b_expires_line = b''
            try:
                for index, b_line in enumerate(b_lines):
                    
                    if b_line.startswith(b'%s:' % b_name):
                        b_passwd_line = b_lines[index + 1]
                        b_expires_line = b_lines[index + 2]
                        break
                
                if b' = ' in b_passwd_line:
                    b_passwd = b_passwd_line.split(b' = ', 1)[-1].strip()
                if b' = ' in b_expires_line:
                    b_expires = b_expires_line.split(b' = ', 1)[-1].strip()
            except IndexError:
                self.module.fail_json(msg='Failed to parse shadow file %s' % self.SHADOWFILE)
        passwd = to_native(b_passwd)
        expires = to_native(b_expires) or -1
        return passwd, expires
class HPUX(User):