Extend CHECKPOINT_LOCK to HSQLDBSaver.execute()

This is used when saving new data to the db, so also needs to be blocked if we are checkpointing or deciding whether to checkpoint.

src/main/java/org/qortal/repository/hsqldb/HSQLDBRepository.java

@@ -55,7 +55,7 @@ public class HSQLDBRepository implements Repository {
 
 	private static final Logger LOGGER = LogManager.getLogger(HSQLDBRepository.class);
 
-	private static final Object CHECKPOINT_LOCK = new Object();
+	public static final Object CHECKPOINT_LOCK = new Object();
 
 	// "serialization failure"
 	private static final Integer DEADLOCK_ERROR_CODE = Integer.valueOf(-4861);

src/main/java/org/qortal/repository/hsqldb/HSQLDBSaver.java

@@ -61,13 +61,15 @@ public class HSQLDBSaver {
 	public boolean execute(HSQLDBRepository repository) throws SQLException {
 		String sql = this.formatInsertWithPlaceholders();
 
-		try {
-			PreparedStatement preparedStatement = repository.prepareStatement(sql);
-			this.bindValues(preparedStatement);
-
-			return preparedStatement.execute();
-		} catch (SQLException e) {
-			throw repository.examineException(e);
+		synchronized (HSQLDBRepository.CHECKPOINT_LOCK) {
+			try {
+				PreparedStatement preparedStatement = repository.prepareStatement(sql);
+				this.bindValues(preparedStatement);
+
+				return preparedStatement.execute();
+			} catch (SQLException e) {
+				throw repository.examineException(e);
+			}
 		}
 	}