Custom commands can't be opened when there are no items in the list

**Custom commands can't be opened when there are no items in the list (containers, images, volumes, services respectively).**

I'm not sure whether this is a bug report or feature request. For my use case, it feels like a bug, but I can see how it could be intended behavior.

**To Reproduce**
Add some custom command to the `~/.config/lazydocker/config.yml`:

```
customCommands:
containers:
- name: My custom command
attach: false
command: '{{ .DockerCompose }} -f /home/user/my-docker-compose.yml up -d'
serviceNames: []
```

On an empty "Containers" list (see screenshot):

1. Highlight the "Containers" area
2. Press the shortcut to open the custom command selection (default: c)
3. Notice the custom command selection does not open

**Expected behaviour**
The custom command selection opens, even when there are no containers in the list.

Ideally, only custom commands that do not depend on a highlighted context item (container, image, volume, service) are listed. The example above does not depend on anything and could run even when no context item is available.

I never used a custom command that depends on a context item of the list, so I'm not sure this is correct, but an example command that I can think of which references an item maybe looks something like: `{{ .DockerCompose }} something something {{ .Container.Name }}` (where .Container.Name is the name of the highlighted container?).

Or, would it perhaps make sense to have a new kind of custom command that's independent of any of the areas?

Or maybe I am using lazydocker wrong, also possible. I really love the custom command feature, but I might be abusing it. Where would I put my small collection of commands that do not depend on a highlighted item?

**Screenshots**

An empty "containers" list:


**Desktop (please complete the following information):**
- OS: Pop!_OS 21.10
- Lazydocker Version 0.12