### 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.groups is None:
            return None
        info = self.user_info()
        groups = set(x.strip() for x in self.groups.split(',') if x)
        for g in groups.copy():
            if not self.group_exists(g):
                self.module.fail_json(msg="Group %s does not exist" % (g))
            if info and remove_existing and self.group_info(g)[2] == info[3]:
                groups.remove(g)
        return groups
    def user_group_membership(self, exclude_primary=True):
        ''' Return a list of groups the user belongs to '''
        groups = []
        info = self.get_pwd_info()
        for group in grp.getgrall():
            if self.name in group.gr_mem:
                
                if not exclude_primary:
                    groups.append(group[0])
                else:
                    if info[3] != group.gr_gid:
                        groups.append(group[0])
        return groups
    def user_exists(self):