### 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 set the user's home directory.
        type: path
    skeleton:
        description:
            - Optionally set a home skeleton directory.
            - Requires C(create_home) option!
        type: str
        version_added: "2.0"
    password:
        description:
            - Optionally set the user's password to this crypted value.
            - On macOS systems, this value has to be cleartext. Beware of security issues.
            - To create a an account with a locked/disabled password on Linux systems, set this to C('!') or C('*').
            - To create a an account with a locked/disabled password on OpenBSD, set this to C('*************').
            - See L(FAQ entry,https://docs.ansible.com/ansible/latest/reference_appendices/faq.html#how-do-i-generate-encrypted-passwords-for-the-user-module)
              for details on various ways to generate these password values.
        type: str
    state:
        description:
            - Whether the account should exist or not, taking action if the state is different from what is stated.
        type: str
        choices: [ absent, present ]
        default: present
    create_home:
        description:
            - Unless set to C(no), a home directory will be made for the user
              when the account is created or if the home directory does not exist.
            - Changed from C(createhome) to C(create_home) in Ansible 2.5.
        type: bool