Settle pending Traffic height work when the population empties

A closure that removes the last animated points mid height correction
released the render hold, and animate() then returned before easeHeights()
could run, leaving _heightPending (and getStats().loading) true. Settle
every retained road on its corrected heights before the hold is released.

Adds a regression combining height correction, a late closure and an
empty population.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/layers/traffic/animation.js

@@ -25,6 +25,9 @@ export function createAnimation({
       layerState._enabled &&
       (layerState._dots.length || layerState._heatJamPrim),
     );
+    // Height easing only runs in a held frame. Settle it before releasing, so
+    // a population emptied mid-correction cannot report loading forever.
+    if (!needed && layerState._heightPending) parts.retention.finishHeights();
     if (needed === Boolean(layerState._renderHeld)) return;
     layerState._renderHeld = needed;
     if (needed) {