Reject overlong encodings earlier

src/ripple/protocol/impl/tokens.cpp

@@ -216,6 +216,10 @@ decodeBase58 (std::string const& s,
         ++psz;
         --remain;
     }
+
+    if (remain > 64)
+        return {};
+
     // Allocate enough space in big-endian base256 representation.
     // log(58) / log(256), rounded up.
     std::vector<unsigned char> b256(