fix sonarlint issues, add IDerivedWaveform interface

plugins/com.minres.scviewer.e4.application/src/com/minres/scviewer/e4/application/parts/LoadingWaveformDb.java

@@ -5,6 +5,7 @@ import java.io.File;
 import java.util.ArrayList;
 import java.util.List;
 
+import com.minres.scviewer.database.IDerivedWaveform;
 import com.minres.scviewer.database.IHierNode;
 import com.minres.scviewer.database.IWaveform;
 import com.minres.scviewer.database.IWaveformDb;
@@ -85,4 +86,9 @@ public class LoadingWaveformDb implements IWaveformDb {
 	public void clear() {
 	}
 
+	@Override
+	public IDerivedWaveform deriveWaveform() {
+		return null;
+	}
+
 }