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: bitcoin#7922
Rebased-From: 5770449

src/base58.cpp

@@ -172,7 +172,7 @@ bool CBase58Data::SetString(const char* psz, unsigned int nVersionBytes)
     vchData.resize(vchTemp.size() - nVersionBytes);
     if (!vchData.empty())
         memcpy(&vchData[0], &vchTemp[nVersionBytes], vchData.size());
-    memory_cleanse(&vchTemp[0], vchData.size());
+    memory_cleanse(&vchTemp[0], vchTemp.size());
     return true;
 }