### 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
version_added: "2.1"
    group:
        description:
            - Optionally sets the user's primary group (takes a group name).
        type: str
    groups:
        description:
            - List of groups user will be added to.
            - By default, the user is removed from all other groups. Configure C(append) to modify this.
            - When set to an empty string C(''),
              the user is removed from all groups except the primary group.
            - Before Ansible 2.3, the only input format allowed was a comma separated string.
        type: list
        elements: str
    append:
        description:
            - If C(yes), add the user to the groups specified in C(groups).
            - If C(no), user will only be added to the groups specified in C(groups),
              removing them from all other groups.
        type: bool
        default: no
    shell:
        description:
            - Optionally set the user's shell.
            - On macOS, before Ansible 2.5, the default shell for non-system users was C(/usr/bin/false).
              Since Ansible 2.5, the default shell for non-system users on macOS is C(/bin/bash).
            - See notes for details on how other operating systems determine the default shell by
              the underlying tool.
        type: str
    home: