Improve TRANSACTION_SIGNATURES handling in Controller.

Don't disconnect peers that fail to send a requested transaction,
as they may no longer have it. e.g. transaction might have expired
or become invalid.

For some other cases, e.g. we have transaction already, move on to
requesting the next transaction instead of giving up on the list.

src/main/java/org/qora/controller/Controller.java

@@ -738,15 +738,16 @@ public class Controller extends Thread {
 						// Do we have it already? (Before requesting transaction data itself)
 						if (repository.getTransactionRepository().exists(signature)) {
 							LOGGER.trace(String.format("Ignoring existing transaction %s from peer %s", Base58.encode(signature), peer));
-							break;
+							continue;
 						}
 
 						// Fetch actual transaction data from peer
 						Message getTransactionMessage = new GetTransactionMessage(signature);
 						Message responseMessage = peer.getResponse(getTransactionMessage);
 						if (responseMessage == null || !(responseMessage instanceof TransactionMessage)) {
-							peer.disconnect("failed to fetch unconfirmed transaction");
-							break;
+							// Maybe peer no longer has this transaction
+							LOGGER.trace(String.format("Peer %s didn't send transaction %s", peer, Base58.encode(signature)));
+							continue;
 						}
 
 						TransactionMessage transactionMessage = (TransactionMessage) responseMessage;
@@ -756,24 +757,25 @@ public class Controller extends Thread {
 						// Check signature
 						if (!transaction.isSignatureValid()) {
 							LOGGER.trace(String.format("Ignoring %s transaction %s with invalid signature from peer %s", transactionData.getType().name(), Base58.encode(transactionData.getSignature()), peer));
-							break;
+							continue;
 						}
 
 						ValidationResult validationResult = transaction.importAsUnconfirmed();
 
 						if (validationResult == ValidationResult.TRANSACTION_ALREADY_EXISTS) {
 							LOGGER.trace(String.format("Ignoring existing transaction %s from peer %s", Base58.encode(transactionData.getSignature()), peer));
-							break;
+							continue;
 						}
 
 						if (validationResult == ValidationResult.NO_BLOCKCHAIN_LOCK) {
 							LOGGER.trace(String.format("Couldn't lock blockchain to import unconfirmed transaction %s from peer %s", Base58.encode(transactionData.getSignature()), peer));
+							// Some other thread (e.g. Synchronizer) might have blockchain lock for a while so might as well give up for now
 							break;
 						}
 
 						if (validationResult != ValidationResult.OK) {
 							LOGGER.trace(String.format("Ignoring invalid (%s) %s transaction %s from peer %s", validationResult.name(), transactionData.getType().name(), Base58.encode(transactionData.getSignature()), peer));
-							break;
+							continue;
 						}
 
 						LOGGER.debug(String.format("Imported %s transaction %s from peer %s", transactionData.getType().name(), Base58.encode(transactionData.getSignature()), peer));