Fixing undefined behavior in lib CRC

[LeStarch]

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Change Description

A lack of casting in libcrc tripped the undefined behavior and address sanitizers when running update_crc_16. This occurs when the result is -1 and passed as an index. By forcing a cast to unsigned int, the index should be guided back into a non-negative range.

Future Work

We should search for and possible baseline a flight-quality implementation of CRCs/