fix: Don't error if $globals.CurrentContainer is nil

[rhansen]

Also:

• Note when there are no networks.
• Fix "networks available" comment.

Fixes #2189

[rhansen]

Can you test this @genestouxguy (or @SchoNie)?

[SchoNie]

It's failing for me with -only-exposed:
Template error: template: nginx.tmpl:29:10: executing "nginx.tmpl" at <sortObjectsByKeysAsc (or $globals.CurrentContainer (dict)).Networks "Name">: error calling sortObjectsByKeysAsc: must pass an array or slice to 'sortObjsByKeys'; received <nil>; kind invalid

[rhansen]

It's failing for me with -only-exposed

That's what I get for hastily tossing the fix together. Thanks for testing @SchoNie. I pushed a new version; would you mind testing it?

[SchoNie]

Confirm now it's OK.
Both scenarios (with and without -only-exposed) tested.