fix(js): do not render empty sections

[shortcuts]

Summary

When having multi-sources, sections without results and noResults template were still rendering their header and/or footer template, which required some extra logic for the user.

Result

Sections without results and noResults template are not rendered anymore.

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Sandbox	Source
@algolia/autocomplete-example-github-repositories-custom-plugin	Configuration
@algolia/autocomplete-example-instantsearch	Configuration
@algolia/autocomplete-example-playground	Configuration
@algolia/autocomplete-example-preview-panel-in-modal	Configuration
@algolia/autocomplete-example-react-renderer	Configuration
@algolia/autocomplete-example-starter-algolia	Configuration
@algolia/autocomplete-example-starter	Configuration
@algolia/autocomplete-example-voice-search	Configuration
@algolia/autocomplete-example-vue	Configuration

[francoischalifour]

That looks good!

We can remove all these checks from our examples now:

autocomplete/examples/playground/categoriesPlugin.tsx

Lines 40 to 42 in b25c140

	if (items.length === 0) {
	return null;
	}

[francoischalifour]

Perfect, that'll reduce user code!