### 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
type: str
    generate_ssh_key:
        description:
            - Whether to generate a SSH key for the user in question.
            - This will B(not) overwrite an existing SSH key unless used with C(force=yes).
        type: bool
        default: no
        version_added: "0.9"
    ssh_key_bits:
        description:
            - Optionally specify number of bits in SSH key to create.
        type: int
        default: default set by ssh-keygen
        version_added: "0.9"
    ssh_key_type:
        description:
            - Optionally specify the type of SSH key to generate.
            - Available SSH key types will depend on implementation
              present on target host.
        type: str
        default: rsa
        version_added: "0.9"
    ssh_key_file:
        description:
            - Optionally specify the SSH key filename.
            - If this is a relative filename then it will be relative to the user's home directory.
            - This parameter defaults to I(.ssh/id_rsa).
        type: path
        version_added: "0.9"
    ssh_key_comment: