don't load parent multiple times into tree when multiple childs are changed

when an action (e.g. moving a way) caused multiple child elements
of the same parent to be changed, their parent was also loaded into
the tree multiple times during `tree.intersects()`.

this fixes #1978
Merge pull request #1980 from tyrasd/patch-fix-delete-after-action

don't load parent into tree repeatedly when multiple childs are changed