### 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
if self.local:
            if not os.path.exists(self.PASSWORDFILE):
                self.module.fail_json(msg="'local: true' specified but unable to find local account file {0} to parse.".format(self.PASSWORDFILE))
            exists = False
            name_test = '{0}:'.format(self.name)
            with open(self.PASSWORDFILE, 'rb') as f:
                reversed_lines = f.readlines()[::-1]
                for line in reversed_lines:
                    if line.startswith(to_bytes(name_test)):
                        exists = True
                        break
            if not exists:
                self.module.warn(
                    "'local: true' specified and user '{name}' was not found in {file}. "
                    "The local user account may already exist if the local account database exists "
                    "somewhere other than {file}.".format(file=self.PASSWORDFILE, name=self.name))
            return exists
        else:
            try:
                if pwd.getpwnam(self.name):
                    return True
            except KeyError:
                return False
    def get_pwd_info(self):