Averaging materials does not work for big particles

if particle volume exceeds some value, assertion

admix.fraction >= 0 && admix.fraction <= 1

fails.

How to check: go to example scatter2d/SlicedLayer.py and increase the radius of sphere ff.

This looks like an error in a logic.

added bug crash labels

removed crash label

added physics label

changed the description

changed milestone to %v22

assigned to @m.svechnikov

not a bug, but the assertion may fail due to wrong user input ==> throw a normal exception instead

mentioned in merge request !2883 (merged)

mentioned in commit dec7f522

closed with merge request !2883 (merged)