LGTM.com - false positive (decrementing uint8_t)

**Description of the false positive**

lgtm is claiming that a loop variable of type `uint8_t` will always stay equal to or greater than its initial value, despite the for-loop decrementing it. It's as if lgtm is not modelling unsigned variables or for loops correctly.

**URL to the alert on the project page on LGTM.com**

https://lgtm.com/projects/g/Chia-Network/chiapos/snapshot/837b9be23d5d21104a41b99fb9b5ad7fd2686e20/files/src/phase2.hpp?sort=name&dir=ASC&mode=heatmap#xb62e750067a5c62f:1