### 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
cmd.append('-k')
                cmd.append(self.skeleton)
            if self.umask is not None:
                cmd.append('-K')
                cmd.append('UMASK=' + self.umask)
        if self.profile is not None:
            cmd.append('-P')
            cmd.append(self.profile)
        if self.authorization is not None:
            cmd.append('-A')
            cmd.append(self.authorization)
        if self.role is not None:
            cmd.append('-R')
            cmd.append(self.role)
        cmd.append(self.name)
        (rc, out, err) = self.execute_command(cmd)
        if rc is not None and rc != 0:
            self.module.fail_json(name=self.name, msg=err, rc=rc)
        if not self.module.check_mode:
            
            if self.password is not None:
                self.backup_shadow()
                minweeks, maxweeks, warnweeks = self.get_password_defaults()
                try:
                    lines = []
                    with open(self.SHADOWFILE, 'rb') as f:
                        for line in f:
                            line = to_native(line, errors='surrogate_or_strict')
                            fields = line.strip().split(':')
                            if not fields[0] == self.name: