fix i256 key type conversion by initialize buffer before usage

plugins/chain_plugin/include/eosio/chain_plugin/chain_plugin.hpp

@@ -941,7 +941,7 @@ class read_write : public api_base {
             // the following will convert the input to array of 2 uint128_t in little endian, i.e. 50f0fa8360ec998f4bb65b00c86282f5 fb54b91bfed2fe7fe39a92d999d002c5
             // which is the format used by secondary index
             chain::key256_t k;
-            uint8_t buffer[32];
+            uint8_t buffer[32] = {};
             boost::multiprecision::export_bits(v, buffer, 8, false);
             memcpy(&k[0], buffer + 16, 16);
             memcpy(&k[1], buffer, 16);