CBase58Data::SetString: cleanse the full vector
CBase58Data::SetString: cleanse the full vector

SetString seems to be passing the length of the wrong variable to
memory_cleanse, resulting in the last byte of the temporary buffer not being
securely erased.

Github-Pull: #7922
Rebased-From: 57704499be948c640c789c7fc11ed1abf8a681bd

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