### 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
default: yes
        aliases: [ createhome ]
    move_home:
        description:
            - "If set to C(yes) when used with C(home: ), attempt to move the user's old home
              directory to the specified directory if it isn't there already and the old home exists."
        type: bool
        default: no
    system:
        description:
            - When creating an account C(state=present), setting this to C(yes) makes the user a system account.
            - This setting cannot be changed on existing users.
        type: bool
        default: no
    force:
        description:
            - This only affects C(state=absent), it forces removal of the user and associated directories on supported platforms.
            - The behavior is the same as C(userdel --force), check the man page for C(userdel) on your system for details and support.
            - When used with C(generate_ssh_key=yes) this forces an existing key to be overwritten.
        type: bool
        default: no
    remove:
        description:
            - This only affects C(state=absent), it attempts to remove directories associated with the user.
            - The behavior is the same as C(userdel --remove), check the man page for details and support.
        type: bool
        default: no
    login_class:
        description:
            - Optionally sets the user's login class, a feature of most BSD OSs.