Fix onHover/tooltip flickering

[Pessimistress]

onHover is called with an empty pickingInfo if the cursor moves from one pickable layer to another.

This only happens to hover events, as we produce a "mouse out" event before the "mouse over":

deck.gl/modules/core/src/lib/picking/pick-info.js

Lines 52 to 55 in b0b7988

	if (lastPickedLayer) {
	// Let leave event fire before enter event
	affectedLayers.unshift(lastPickedLayer);
	}

Change List

• Call onHover/getTooltip with a picked info if any

[coveralls]

Coverage decreased (-2.9%) to 80.137% when pulling b4c79b7 on x/picking-fix into 8af69dc on master.