Empty molecule.yml when using --base-config

# Issue Type

- Bug report

# Molecule and Ansible details

```
ansible --version && molecule --version

molecule 4.0.4 using python 3.9
ansible:2.14.1
delegated:4.0.4 from molecule
docker:2.1.0 from molecule_docker requiring collections: community.docker>=3.0.2 ansible.posix>=1.4.0
```

Molecule installation method (one of):
- pip

Ansible installation method (one of):
- pip

# Desired Behavior

I'm using `--base-config` in order to abstract all the content of `molecule.yml`. This allow me to not duplicate otherwise identical content in all my roles.

Unfortunately I still need to keep an almost empty file in `/molecule/default/molecule.yml`. It would be a lot cleaner if I can remove completely the file `molecule.yml` from inside the role and only keep the global one.

# Actual Behaviour

If I try to test a role without a molecule.yml I have the following error:

```
CRITICAL 'molecule/*/molecule.yml' glob failed. Exiting.
```

Start by reproducing the failure with Molecule 4.0.4 and --base-config using a role that has no molecule/default/molecule.yml. Trace the code path producing the 'molecule/*/molecule.yml' glob failure, then verify that a global base configuration can run without the per-role file while preserving existing behavior.

Written by the indexing model from the issue text.