There is an assert in `CWalletTx::RelayWalletTransaction` that gets hit.  All other code paths check `fBroadcastTransactions` before getting to `CWallet::ResendWalletTransactionsBefore` except the rpc call `resendwalletransactions`.

It's an easy fix, but we just need to decide whether to throw an error or return an empty array of rebroadcasted transaction ids.

Should be fixed for 0.15.
+ HelpExampleCli("listunspent", "") +
            "\nLock an unspent transaction\n"
            + HelpExampleCli("lockunspent", "false \"[{\\\"txid\\\":\\\"a08e6907dbbd3d809776dbfc5d82e371b764ed838b5655e72f463568df1aadf0\\\",\\\"vout\\\":1}]\"") +
            "\nList the locked transactions\n"
            + HelpExampleCli("listlockunspent", "") +
            "\nUnlock the transaction again\n"
            + HelpExampleCli("lockunspent", "true \"[{\\\"txid\\\":\\\"a08e6907dbbd3d809776dbfc5d82e371b764ed838b5655e72f463568df1aadf0\\\",\\\"vout\\\":1}]\"") +
            "\nAs a json rpc call\n"
            + HelpExampleRpc("lockunspent", "false, \"[{\\\"txid\\\":\\\"a08e6907dbbd3d809776dbfc5d82e371b764ed838b5655e72f463568df1aadf0\\\",\\\"vout\\\":1}]\"")
        );
    LOCK2(cs_main, pwallet->cs_wallet);
    if (request.params.size() == 1)
        RPCTypeCheck(request.params, {UniValue::VBOOL});
    else
        RPCTypeCheck(request.params, {UniValue::VBOOL, UniValue::VARR});
    bool fUnlock = request.params[0].get_bool();
    if (request.params.size() == 1) {
        if (fUnlock)
            pwallet->UnlockAllCoins();
        return true;
    }
    UniValue outputs = request.params[1].get_array();
    for (unsigned int idx = 0; idx < outputs.size(); idx++) {
        const UniValue& output = outputs[idx];
        if (!output.isObject())
            throw JSONRPCError(RPC_INVALID_PARAMETER, "Invalid parameter, expected object");
        const UniValue& o = output.get_obj();
        RPCTypeCheckObj(o,
            {
                {"txid", UniValueType(UniValue::VSTR)},