to material in a child cell, and the label is a point or line label,
and the parent cell has no material other than the label in the
immediate area, then the "interaction area" will have zero area,
which will cause problems as area checks on a zero-sized area don't
do anything useful. The solution is to ensure that interaction areas
do not have zero area, but will expand around point labels. This
should not have any other implications, because the interaction area
is just a way to limit the amount of processing; larger interaction
areas do not affect the extraction result (except in this case, where
it fixes the error).
04e91d640d