### 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
description:
            - Optionally define the comment for the SSH key.
        type: str
        default: ansible-generated on $HOSTNAME
        version_added: "0.9"
    ssh_key_passphrase:
        description:
            - Set a passphrase for the SSH key.
            - If no passphrase is provided, the SSH key will default to having no passphrase.
        type: str
        version_added: "0.9"
    update_password:
        description:
            - C(always) will update passwords if they differ.
            - C(on_create) will only set the password for newly created users.
        type: str
        choices: [ always, on_create ]
        default: always
        version_added: "1.3"
    expires:
        description:
            - An expiry time for the user in epoch, it will be ignored on platforms that do not support this.
            - Currently supported on GNU/Linux, FreeBSD, and DragonFlyBSD.
            - Since Ansible 2.6 you can remove the expiry time by specifying a negative value.
              Currently supported on GNU/Linux and FreeBSD.
        type: float
        version_added: "1.9"
    password_lock:
        description:
            - Lock the password (C(usermod -L), C(usermod -U), C(pw lock)).