fix(clearRefinements): do not throw when widgetParams is not given

[eunjae-lee]

Summary

This PR prevents connectClearRefinement from throwing an error when widgetParams is not given.
When it's used with the official clearRefinement widget, then normally at least container is there, but if it's used in a custom widget or in Vue InstantSearch, there could be no widgetParams at all.

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[Haroenv]

Vue InstantSearch

Doesn't Vue InstantSearch always at least give an empty object since it's calculated from props? This PR still makes sense, but I'm not sure whether Vue InstantSearch is relevant

[eunjae-lee]

Vue InstantSearch

Doesn't Vue InstantSearch always at least give an empty object since it's calculated from props? This PR still makes sense, but I'm not sure whether Vue InstantSearch is relevant

Our official widgets provide an empty object, but if it's a custom widget and the one who made the widget didn't provide an empty object, it will fail, which was the case in the e-commerce demo in Vue InstantSearch.