Fix issue #112, NPE in RocketFigure3d mouseDragged()

The component can pick up a mouse drag event without a mouse press event
if the mous is clicked and dragged while a modal dialog is open. The
running simulations progress bar dialog is an example. To fix, do not
process a mouse drag if a mouse press has not been recorded.

core/src/net/sf/openrocket/gui/figure3d/RocketFigure3d.java

@@ -234,6 +234,10 @@ public class RocketFigure3d extends JPanel implements GLEventListener {
 			
 			@Override
 			public void mouseDragged(final MouseEvent e) {
+				//You can get a drag without a press while a modal dialog is shown
+				if (pressEvent == null)
+					return;
+				
 				int dx = lastX - e.getX();
 				int dy = lastY - e.getY();
 				lastX = e.getX();