OSV-2020-1170 Heap-buffer-overflow in arrow::internal::CountSetBits

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=20199 Crash type: Heap-buffer-overflow READ 8 Crash state: arrow::internal::CountSetBits arrow::Array::nullcount arrow::internal::ValidateArray...