land-cover-completeness: result above 100 percent when polygons overlap

[Gigaszi]

Example: https://ohsome.org/apps/dashboard-test/#backend=oqtApi&topic=land-cover&bboxes=4.1440437%2C47.2798206%2C4.1445477%2C47.2802829&indicators=land-cover-completeness
(natural=wood and natural=water overlapp)