VG-9732 Avoid 503 error on explorer /timestamp (#932)

* VG-9732 Avoid 503 error on explorer /timestamp

Author: BertrandD

core/src/wallet/bitcoin/transaction_builders/BitcoinLikeUtxoPicker.cpp

@@ -155,12 +155,13 @@ namespace ledger {
                 return Future<Unit>::successful(unit);
             }
             // Set timestamp
-            buddy->explorer->getTimestamp().onComplete(getContext(), [=](const Try<int64_t> &timestamp) {
-                if (timestamp.isSuccess()) {
-                    buddy->transaction->setTimestamp(timestamp.getValue());
-                }
-            });
-
+            if (_currency.bitcoinLikeNetworkParameters->UsesTimestampedTransaction) {
+                buddy->explorer->getTimestamp().onComplete(getContext(), [=](const Try<int64_t> &timestamp) {
+                    if (timestamp.isSuccess()) {
+                        buddy->transaction->setTimestamp(timestamp.getValue());
+                    }
+                });
+            }
             return buddy->explorer->getCurrentBlock().map<Unit>(getContext(), [=](const std::shared_ptr<BitcoinLikeBlockchainExplorer::Block> &block) -> Unit {
                 buddy->transaction->setLockTime(static_cast<uint32_t>(block->height));
                 return unit;