### 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
non_unique=dict(type='bool', default=False),
            group=dict(type='str'),
            groups=dict(type='list', elements='str'),
            comment=dict(type='str'),
            home=dict(type='path'),
            shell=dict(type='str'),
            password=dict(type='str', no_log=True),
            login_class=dict(type='str'),
            password_expire_max=dict(type='int', no_log=False),
            password_expire_min=dict(type='int', no_log=False),
            
            hidden=dict(type='bool'),
            
            seuser=dict(type='str'),
            
            force=dict(type='bool', default=False),
            remove=dict(type='bool', default=False),
            
            create_home=dict(type='bool', default=True, aliases=['createhome']),
            skeleton=dict(type='str'),
            system=dict(type='bool', default=False),
            
            move_home=dict(type='bool', default=False),
            append=dict(type='bool', default=False),
            
            generate_ssh_key=dict(type='bool'),
            ssh_key_bits=dict(type='int', default=ssh_defaults['bits']),
            ssh_key_type=dict(type='str', default=ssh_defaults['type']),
            ssh_key_file=dict(type='path'),
            ssh_key_comment=dict(type='str', default=ssh_defaults['comment']),