Use prefix operator in for loop of DecodeBase58.

Author: wjx

src/base58.cpp

@@ -42,7 +42,7 @@ bool DecodeBase58(const char* psz, std::vector<unsigned char>& vch)
         // Apply "b256 = b256 * 58 + ch".
         int carry = ch - pszBase58;
         int i = 0;
-        for (std::vector<unsigned char>::reverse_iterator it = b256.rbegin(); (carry != 0 || i < length) && (it != b256.rend()); it++, i++) {
+        for (std::vector<unsigned char>::reverse_iterator it = b256.rbegin(); (carry != 0 || i < length) && (it != b256.rend()); ++it, ++i) {
             carry += 58 * (*it);
             *it = carry % 256;
             carry /= 256;