Fix AB4 main loop

Signed-off-by: Lorenz Stechauner <lorenz.stechauner@necronda.net>

src/Simulation4.java

@@ -36,9 +36,7 @@ public class Simulation4 {
         while (true) {
             seconds++;
 
-            for (Body b : sol.getBodies()) {
-                sol.addForceFrom(b);
-            }
+            sol.addForceTo(sol);
             sol.update();
 
             if ((seconds % 3600) == 0) {