When synchronizing, filter out peers that have a recent block with an invalid signer.

This avoids the wasted time and consensus confusion causes by syncing and then validation failing. This is significant after the algo has run, as many signers will become invalid.

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

@@ -29,6 +29,7 @@ import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 import org.bouncycastle.jce.provider.BouncyCastleProvider;
 import org.bouncycastle.jsse.provider.BouncyCastleJsseProvider;
+import org.qortal.account.Account;
 import org.qortal.api.ApiService;
 import org.qortal.api.DomainMapService;
 import org.qortal.api.GatewayService;
@@ -756,6 +757,27 @@ public class Controller extends Thread {
 		return peer.isAtLeastVersion(minPeerVersion) == false;
 	};
 
+	public static final Predicate<Peer> hasInvalidSigner = peer -> {
+		final List<BlockSummaryData> peerChainTipSummaries = peer.getChainTipSummaries();
+		if (peerChainTipSummaries == null) {
+			return true;
+		}
+
+		try (Repository repository = RepositoryManager.getRepository()) {
+			for (BlockSummaryData blockSummaryData : peerChainTipSummaries) {
+				if (Account.getRewardShareEffectiveMintingLevel(repository, blockSummaryData.getMinterPublicKey()) == 0) {
+					return true;
+				}
+			}
+		} catch (DataException e) {
+			return true;
+		}
+
+		// We got this far without encountering invalid or missing summaries, nor was an exception thrown,
+		// so it is safe to assume that all of this peer's recent blocks had a valid signer.
+		return false;
+	};
+
 	private long getRandomRepositoryMaintenanceInterval() {
 		final long minInterval = Settings.getInstance().getRepositoryMaintenanceMinInterval();
 		final long maxInterval = Settings.getInstance().getRepositoryMaintenanceMaxInterval();

src/main/java/org/qortal/controller/Synchronizer.java

@@ -247,6 +247,9 @@ public class Synchronizer extends Thread {
 		// Disregard peers that are on the same block as last sync attempt and we didn't like their chain
 		peers.removeIf(Controller.hasInferiorChainTip);
 
+		// Disregard peers that have a block with an invalid signer
+		peers.removeIf(Controller.hasInvalidSigner);
+
 		final int peersBeforeComparison = peers.size();
 
 		// Request recent block summaries from the remaining peers, and locate our common block with each