hasData update

Author: karlnicholas

src/main/java/org/hdf5javalib/hdfjava/HdfDataset.java

@@ -352,6 +352,7 @@ public synchronized ByteBuffer getDatasetData(SeekableByteChannel channel, long
     public boolean hasData() {
         return hardLink == null
             && hasDataspaceMessage()
+            && objectHeader.findMessageByType(DatatypeMessage.class).isPresent()
             && objectHeader.findMessageByType(DataLayoutMessage.class).orElseThrow().hasData();
     }