cubicweb #12512052 internal error message appears in UI when facets search has no result [open]

eg search for whatever in the plain text facet of, you'll see a NoSelectableObject: args: (,), kwargs: ['rset'] candidates: [] message appears on top of the "no result message".

This is because the facet attempt to reload the edit box which is not selectable on empty rset. We should either handle that at the js level or make the render python callback return an empty string on no selectable object.

done in<not specified>
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