

Using bitcoin-cli in order to generate a transaction with two op_return generate a wrong transaction.

```
bitcoin-cli createrawtransaction "[]" "{\"data\":\"ee\", \"data\":\"ff\"}"
0200000000020000000000000000036a01ee0000000000000000036a01ee00000000
```

Decoding the hex I obtain the following transaction with two op_return with the same value.

```
bitcoin-cli decoderawtransaction "0200000000020000000000000000036a01ee0000000000000000036a01ee00000000"
{
  "txid": "ed4b691958a573c8569177606c77905ecd07c36eb5eec443f17a45427bb9f5fc",
  "hash": "ed4b691958a573c8569177606c77905ecd07c36eb5eec443f17a45427bb9f5fc",
  "version": 2,
  "size": 34,
  "vsize": 34,
  "weight": 136,
  "locktime": 0,
  "vin": [
  ],
  "vout": [
    {
      "value": 0.00000000,
      "n": 0,
      "scriptPubKey": {
        "asm": "OP_RETURN -110",
        "hex": "6a01ee",
        "type": "nulldata"
      }
    },
    {
      "value": 0.00000000,
      "n": 1,
      "scriptPubKey": {
        "asm": "OP_RETURN -110",
        "hex": "6a01ee",
        "type": "nulldata"
      }
    }
  ]
}
```

This incorrect behavior is related to the duplicate key "data" in the JSON passed to the "createrawtransaction" command.

The problem is related to the use of `outputs[name_].getValStr()` in an JSON with duplicated keys https://github.com/bitcoin/bitcoin/blob/master/src/rpc/rawtransaction.cpp#L432

Although this kind of transaction wouldn't be relayed, I thought about two possible solutions:
* raise an error as it happens for the use of two identical addresses, maybe calling `JSONRPCError(RPC_INVALID_PARAMETER ...` if more than one "data" field is recognized - easier to implement, 
* creation of the transaction correctly containing the two different op_returns, maybe need to pass one array in the data field of the passed JSON (like `"data": ["ee", "ff"]`) - maybe require API change.
{
    BOOST_CHECK_THROW(AmountFromValue(ValueFromString("-0.00000001")), UniValue);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0")), 0LL);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.00000000")), 0LL);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.00000001")), 1LL);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.17622195")), 17622195LL);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.5")), 50000000LL);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.50000000")), 50000000LL);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.89898989")), 89898989LL);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("1.00000000")), 100000000LL);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("20999999.9999999")), 2099999999999990LL);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("20999999.99999999")), 2099999999999999LL);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("1e-8")), COIN/100000000);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.1e-7")), COIN/100000000);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.01e-6")), COIN/100000000);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.0000000000000000000000000000000000000000000000000000000000000000000000000001e+68")), COIN/100000000);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("10000000000000000000000000000000000000000000000000000000000000000e-64")), COIN);
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000000000000000000000000000000e64")), COIN);
    BOOST_CHECK_THROW(AmountFromValue(ValueFromString("1e-9")), UniValue); 
    BOOST_CHECK_THROW(AmountFromValue(ValueFromString("0.000000019")), UniValue); 
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.00000001000000")), 1LL); 
    BOOST_CHECK_THROW(AmountFromValue(ValueFromString("19e-9")), UniValue); 
    BOOST_CHECK_EQUAL(AmountFromValue(ValueFromString("0.19e-6")), 19); 
    BOOST_CHECK_THROW(AmountFromValue(ValueFromString("92233720368.54775808")), UniValue); 
    BOOST_CHECK_THROW(AmountFromValue(ValueFromString("1e+11")), UniValue); 
    BOOST_CHECK_THROW(AmountFromValue(ValueFromString("1e11")), UniValue); 
    BOOST_CHECK_THROW(AmountFromValue(ValueFromString("93e+9")), UniValue); 
}
BOOST_AUTO_TEST_CASE(json_parse_errors)