### 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
passwd = ''
        expires = ''
        if os.path.exists(self.SHADOWFILE) and os.access(self.SHADOWFILE, os.R_OK):
            with open(self.SHADOWFILE, 'r') as f:
                for line in f:
                    if line.startswith('%s:' % self.name):
                        passwd = line.split(':')[1]
                        expires = line.split(':')[self.SHADOWFILE_EXPIRE_INDEX] or -1
        return passwd, expires
    def get_ssh_key_path(self):
        info = self.user_info()
        if os.path.isabs(self.ssh_file):
            ssh_key_file = self.ssh_file
        else:
            if not os.path.exists(info[5]) and not self.module.check_mode:
                raise Exception('User %s home directory does not exist' % self.name)
            ssh_key_file = os.path.join(info[5], self.ssh_file)
        return ssh_key_file
    def ssh_key_gen(self):