libnet: don't check if ctrler store is nil

[akerouanton]

- What I did

Since commit befff0e, (*Controller).getStore() never returns nil except if c.store isn't initialized yet. This can't happen unless New() returned an error and it wasn't proper caught.

- How to verify it

CI

[thaJeztah]

Looks like we may be able to clean up more (in a follow-up); let me jot down some things I noticed;

Perhaps we should remove Controller.initStores(). It looks like it's ONLY called from New(), so it would be clearer to be part of that constructor. It also currently has a if c.cfg == nil check, which should belong there if it should never have an empty config; currently reading that code may lead to the assumption that the store COULD be nil (no config), and that not producing an error;

moby/libnetwork/store.go

Lines 13 to 24 in 4554d87

	func (c *Controller) initStores() error {
	if c.cfg == nil {
	return nil
	}
	var err error
	c.store, err = datastore.New(c.cfg.Scope)
	if err != nil {
	return err
	}
	return nil
	}

But looking at the constructor, it can never be nil, so that nil-check is redundant (and deceiving);

moby/libnetwork/controller.go

Line 111 in 4554d87

cfg: config.New(cfgOptions...),

Based on this PR, perhaps Controller.closeStores() is also overly cautious and could have the nil-check removed;

moby/libnetwork/store.go

Lines 26 to 30 in 4554d87

	func (c *Controller) closeStores() {
	if store := c.store; store != nil {
	store.Close()
	}
	}

And, finally, perhaps we should consider reducing use of Controller.getStore() when used internally; it looks like it does not do any synchronisation (which, if it's set in the constructor, and never mutated, wouldn't be needed), which means that checks like the one below are also redundant (and could just be using c.store directly;

moby/libnetwork/store.go

Lines 48 to 53 in 4554d87

	store := c.getStore()
	if store == nil {
	return nil, nil
	}
	kvol, err := store.List(&Network{ctrlr: c})

[thaJeztah]

LGTM