EddyEditor: trile selection can leak behind visible triles

[Krzyhau]

While having a trile already selected, clicking another on a same plane where selection is can lead to it "leaking" and selecting a trile behind it. Presumably it's caused by the "select next one behind" behaviour we've implemented some time ago.

20260619-0832-23.4691414.mp4

[zrckr]

I think that this behavior should be checked again after 524841d rewrite. I can't reproduce it.