Force a bootstrap if the block archive isn't intact on launch

This allows the topOnly setting to be disabled and the node will automatically bootstrap to the archive version. A rebuild isn't attempted if bootstrapping is disabled, in order to reduce risk.

src/main/java/org/qortal/block/BlockChain.java

@@ -502,13 +502,22 @@ public class BlockChain {
 	 */
 	public static void validate() throws DataException {
 
+		boolean isTopOnly = Settings.getInstance().isTopOnly();
+		boolean archiveEnabled = Settings.getInstance().isArchiveEnabled();
+		boolean canBootstrap = Settings.getInstance().getBootstrap();
+		boolean needsArchiveRebuild = false;
 		BlockData chainTip;
+
 		try (final Repository repository = RepositoryManager.getRepository()) {
 			chainTip = repository.getBlockRepository().getLastBlock();
+
+			// Ensure archive is (at least partially) intact, and force a bootstrap if it isn't
+			if (!isTopOnly && archiveEnabled && canBootstrap) {
+				needsArchiveRebuild = (repository.getBlockArchiveRepository().fromHeight(2) == null);
+				LOGGER.info("Couldn't retrieve block 2 from archive. Bootstrapping...");
+			}
 		}
 
-		boolean isTopOnly = Settings.getInstance().isTopOnly();
-		boolean archiveEnabled = Settings.getInstance().isArchiveEnabled();
 		boolean hasBlocks = (chainTip != null && chainTip.getHeight() > 1);
 
 		if (isTopOnly && hasBlocks) {
@@ -516,7 +525,7 @@ public class BlockChain {
 			// It's best not to validate it, and there's no real need to
 		} else {
 			// Check first block is Genesis Block
-			if (!isGenesisBlockValid()) {
+			if (!isGenesisBlockValid() || needsArchiveRebuild) {
 				try {
 					rebuildBlockchain();