Memory leak and saturated memory usage for high values of frustrum

[gpaar]

On larger (e.g. Jezero HiRise data sets), frustrum settings higher than ~30 lead to extensively growing memory usage which seems to saturate at about 33 GBytes. The process stalls and/or crashes at this point.
Seemingly, LoDs are not properly handled and a much larger portion is attempted to load than necessary for the given FoV.
Still present in 4.21.0-Prerelease3