### 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
ssh_key_file = self.get_ssh_key_path()
        if not os.path.exists(ssh_key_file):
            return (1, 'SSH Key file %s does not exist' % ssh_key_file, '')
        cmd = [self.module.get_bin_path('ssh-keygen', True)]
        cmd.append('-l')
        cmd.append('-f')
        cmd.append(ssh_key_file)
        return self.execute_command(cmd, obey_checkmode=False)
    def get_ssh_public_key(self):
        ssh_public_key_file = '%s.pub' % self.get_ssh_key_path()
        try:
            with open(ssh_public_key_file, 'r') as f:
                ssh_public_key = f.read().strip()
        except IOError:
            return None
        return ssh_public_key
    def create_user(self):
        
        return self.create_user_useradd()
    def remove_user(self):
        
        return self.remove_user_userdel()
    def modify_user(self):
        
        return self.modify_user_usermod()
    def create_homedir(self, path):