Geometry Nodes tree always visible

If the GN modifier is not the one selected in the modifier stack, the node tree is not visible in the node editor. While this was made for when we have more than one GN modifier added to our object, it's incovenient to have to select it every time even if it's the only one.

I propose that if the object has only one GN modifier, even if it's not selected in the modifer stack it should always be visible in the node editor.