things being held inside the spatial grid while they should be deleted causes a rareish unit test failure for create_and_destroy. hopefully this fixes it by checking for if the entering movable is being qdeleted as well as early returning in enter_cell if the spatial grid isnt initialized.
Im not sure what exactly causes the hanging refs, but i suspect its something to do with not properly catching qdeleting objects if they for whatever reason enter another part of the spatial grid instead of nullspacing.
This will give us a better idea of what kind of failure we're dealing with -Lemon
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