fitBounds does nothing for one point and zooms to the world for many

• bounds.getSouthWest() and getNorthEast() both return LatLng {lat: 39.907, lng: 116.391}, the same corner twice.
• A multi-point fitBounds ends at zoom 2 with the entire world visible.
• No error is thrown in either case.

1. Print bounds.toBBoxString(), map.getSize() and getZoom() before and after the call.
2. Check whether the bounds is a single point or empty.
3. Check whether coordinates were passed as [lng, lat] instead of [lat, lng].
4. Check map.getSize().y for zero and whether a flyTo animation is still running.

Use map.setView(latlng, 15) for single points, or pad the point into a 0.002 degree box and fitBounds with { padding: [40, 40], maxZoom: 16 }, calling invalidateSize first when the container is zero-sized.

console.log(bounds.isValid());      // true
console.log(bounds.getSouthWest(), bounds.getNorthEast());
// LatLng {lat: 39.907, lng: 116.391} LatLng {lat: 39.907, lng: 116.391}   ← 两个角相同

console.log('bounds', bounds.toBBoxString());
console.log('size', map.getSize());
console.log('zoom before', map.getZoom());

map.fitBounds(bounds);
console.log('zoom after', map.getZoom());

• Passing maxZoom without padding leaves markers at the edge half outside the viewport.
• Calling fitBounds repeatedly during a flyTo animation merges the calls and the final view is not the requested one.