Fix unintended high memory usage#4626
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Cyan4973
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In particular parameter configurations of Zstd, a significantly larger value is used for hashLog than expected.
When hashLog == 0 and params->windowLog < params->hashRateLog, subtraction underflows and this results in using the maximum value for hashLog. This uses a large amount of memory in unintended scenarios.
Adds a unittest for this set of parameters and fixes the issue.