setLatLng adds marker back to map when hidden using LayerControl

[divadsn]

• I'm reporting a bug, not asking for help
• I'm sure this is a Leaflet.MarkerCluster code issue, not an issue with my own code nor with the framework I'm using (Cordova, Ionic, Angular, React…)
• I've searched through the issues to make sure it's not yet reported

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• Leaflet version I'm using: 1.9.4
• Leaflet.MarkerCluster version I'm using: latest from master
• Browser (with version) I'm using: Firefox 121 (although it's not a browser related issue)
• OS/Platform (with version) I'm using: Windows 10

How to reproduce

• Create a map and add markerClusterGroup
• Create LayerControl with L.Control.Layers and add to map
• Add layerGroup to MCG and LayerControl
• Create new marker, add to layerGroup
• Hide the layer using the LayerControl
• Change the latlng of the marker to map.getCenter() for example
• The marker will re-appear despite the layer being hidden!

What behaviour I'm expecting and which behaviour I'm seeing

I've reproduced the same using the LayerControl demo, the marker did not re-appear using the same approach from above.

I found this to be the cause of the bug: https://github.com/Leaflet/Leaflet.markercluster/blob/master/src/MarkerClusterGroup.js#L716

This causes the layer to be re-added, without checking if it's added or not.