Combining 2 atlases should provide 2 identical atlases instead of just one

[CapoFantasma97]

Combining two opened atlases produces just one resulting atlas, instead of providing the two of them with updated contents. Merging an opened atlas with an empty one instead provides two resulting atlases with duplicated content.

This seems counterintuitive: the resulting amount of items depends on whether one of the atlases has been opened or not.

I like the idea of sharing exploration info with friends and the physical interactions provided by Antique Atlas, as opposed to the typical minimap/map hud mods. It'd be nice to have at least an option to enable this behavior, where combining two atlases doesn't produce a single one but instead updates them both with each other's contents.