##### SUMMARY
<!--- Explain the problem briefly below -->
with_first_found fails "No file was found when using first_found. ..." even if a file matches search conditions, when an undefined variable is used in files parameter.
This is started after I've upgraded from ansible 2.8 to 2.9, so I suppose it is a bug.

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
first_found

##### ANSIBLE VERSION
```paste below
ansible 2.9.10
  config file = None
  configured module search path = ['/Users/afunix/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/local/Cellar/ansible/2.9.10/libexec/lib/python3.8/site-packages/ansible
  executable location = /usr/local/bin/ansible
  python version = 3.8.4 (default, Jul 14 2020, 02:58:48) [Clang 11.0.3 (clang-1103.0.32.62)]
```

##### CONFIGURATION
<!--- Paste verbatim output from "ansible-config dump --only-changed" between quotes -->
```paste below
DEFAULT_VAULT_PASSWORD_FILE(env: ANSIBLE_VAULT_PASSWORD_FILE) = /Users/afunix/.vault
```

##### OS / ENVIRONMENT
Host: macOS 10.15.5
Target: CentOS 7.8


##### STEPS TO REPRODUCE

playbook.yml
```yaml
---
- hosts: all
  roles:
      - test

```

roles/test/tasks/main.yml
```yaml
---
- debug:
      msg: "path: {{role_path}}/vars"

- debug:
    msg: "file: {{ansible_distribution}}-{{ansible_distribution_major_version}}.yml"

- name: Load variables specific for OS family
  include_vars: "{{item}}"
  with_first_found:
    - files:
        - "{{ansible_lsb.id}}-{{ansible_lsb.major_release}}.yml"
        - "{{ansible_distribution}}-{{ansible_distribution_major_version}}.yml"
      paths:
        - "{{role_path}}/vars"

```


roles/test/vars/CentOS-7.yml
```yaml
---
test: test
```


##### EXPECTED RESULTS
ansible-playbook is able to find CentOS-7.yml when running against CentOS 7.8 system, since the file exists.


##### ACTUAL RESULTS
ansible-playbook cannot find CentOS-7.yml when running against CentOS 7.8 system.

The issue goes away once I remove "{{ansible_lsb.id}}-{{ansible_lsb.major_release}}.yml" from files.

Checked ansible -m setup for the host and ansible_lsb is empty.

```paste below
$ ansible-playbook -i inventory playbook.yml 

PLAY [all] *****************************************************************************************************************************************************************************************************

TASK [Gathering Facts] *****************************************************************************************************************************************************************************************
ok: [alice]

TASK [test : debug] ********************************************************************************************************************************************************************************************
ok: [alice] => {
    "msg": "path: /Users/afunix/tmp/ansible-with-first-found/roles/test/vars"
}

TASK [test : debug] ********************************************************************************************************************************************************************************************
ok: [alice] => {
    "msg": "file: CentOS-7.yml"
}

TASK [test : Load variables specific for OS family] ************************************************************************************************************************************************************
fatal: [alice]: FAILED! => {"msg": "No file was found when using first_found. Use errors='ignore' to allow this task to be skipped if no files are found"}

PLAY RECAP *****************************************************************************************************************************************************************************************************
alice                      : ok=3    changed=0    unreachable=0    failed=1    skipped=0    rescued=0    ignored=0   

$ stat /Users/afunix/tmp/ansible-with-first-found/roles/test/vars/CentOS-7.yml
16777220 38020305 -rw-r--r-- 1 afunix staff 0 15 "Jul 20 18:11:55 2020" "Jul 20 18:11:38 2020" "Jul 20 18:11:38 2020" "Jul 20 18:11:38 2020" 4096 8 0 /Users/afunix/tmp/ansible-with-first-found/roles/test/vars/CentOS-7.yml

$ ansible -i inventories/production/hosts -m setup alice | grep ansible_lsb
        "ansible_lsb": {},
```

'''
        Runs the task with the loop items specified and collates the result
        into an array named 'results' which is inserted into the final result
        along with the item for which the loop ran.
        '''
        task_vars = self._job_vars
        templar = Templar(loader=self._loader, variables=task_vars)
        self._task.loop_control.post_validate(templar=templar)
        loop_var = self._task.loop_control.loop_var
        index_var = self._task.loop_control.index_var
        loop_pause = self._task.loop_control.pause
        extended = self._task.loop_control.extended
        extended_allitems = self._task.loop_control.extended_allitems
        
        label = self._task.loop_control.label or '{{' + loop_var + '}}'
        if loop_var in task_vars:
            display.warning(u"%s: The loop variable '%s' is already in use. "
                            u"You should set the `loop_var` value in the `loop_control` option for the task"
                            u" to something else to avoid variable collisions and unexpected behavior." % (self._task, loop_var))
        ran_once = False
        task_fields = None
        no_log = False
        items_len = len(items)