travis run: https://travis-ci.org/bitcoin/bitcoin/jobs/406813397

```
rpc_psbt.py failed, Duration: 4 s
stdout:
2018-07-22T13:28:57.765000Z TestFramework (INFO): Initializing test directory /tmp/bitcoin_test_runner_20180722_132530/rpc_psbt_49
2018-07-22T13:29:00.531000Z TestFramework (ERROR): Assertion failed
Traceback (most recent call last):
  File "/home/travis/build/bitcoin/bitcoin/build/bitcoin-x86_64-unknown-linux-gnu/test/functional/test_framework/test_framework.py", line 160, in main
    self.run_test()
  File "/home/travis/build/bitcoin/bitcoin/build/bitcoin-x86_64-unknown-linux-gnu/test/functional/rpc_psbt.py", line 101, in run_test
    assert_raises_rpc_error(-22, "TX decode failed", self.nodes[0].converttopsbt, signedtx['hex'])
  File "/home/travis/build/bitcoin/bitcoin/build/bitcoin-x86_64-unknown-linux-gnu/test/functional/test_framework/util.py", line 105, in assert_raises_rpc_error
    assert try_rpc(code, message, fun, *args, **kwds), "No exception raised"
AssertionError: No exception raised
{
    if (request.fHelp || request.params.size() != 1) {
        throw std::runtime_error(
            RPCHelpMan{"utxoupdatepsbt",
            "\nUpdates a PSBT with witness UTXOs retrieved from the UTXO set or the mempool.\n",
            {
                {"psbt", RPCArg::Type::STR, RPCArg::Optional::NO, "A base64 string of a PSBT"}
            },
            RPCResult {
                "  \"psbt\"          (string) The base64-encoded partially signed transaction with inputs updated\n"
            },
            RPCExamples {
                HelpExampleCli("utxoupdatepsbt", "\"psbt\"")
            }}.ToString());
    }
    RPCTypeCheck(request.params, {UniValue::VSTR}, true);
    
    PartiallySignedTransaction psbtx;
    std::string error;
    if (!DecodeBase64PSBT(psbtx, request.params[0].get_str(), error)) {
        throw JSONRPCError(RPC_DESERIALIZATION_ERROR, strprintf("TX decode failed %s", error));
    }
    
    CCoinsView viewDummy;
    CCoinsViewCache view(&viewDummy);
    {
        LOCK2(cs_main, mempool.cs);
        CCoinsViewCache &viewChain = *pcoinsTip;
        CCoinsViewMemPool viewMempool(&viewChain, mempool);