dask HLL hyperloglog.py nunique_approx resource consumption

A flaw has been found in dask up to 3.0. Affected by this issue is the function nunique_approx of the file dask/dataframe/hyperloglog.py of the component HLL Handler. This manipulation causes resource consumption. The attack is possible to be carried out remotely. A high degree of complexity is needed for the attack. The exploitation is known to be difficult. The pull request to fix this issue awaits acceptance.