Fixes negative/0 simulation intervals

src/main/java/de/tu_darmstadt/tk/SmartHomeNetworkSim/core/SimulationManager.java

@@ -265,7 +265,10 @@ public class SimulationManager extends Observable {
 	 *            duration in milliseconds of a step
 	 */
 	public void setStepDuration(long duration) {
-		this.duration = duration;
+		if(duration>0)
+			this.duration = duration;
+		else
+			this.duration = 1;
 		notifyPanels();
 	}
 

src/main/java/de/tu_darmstadt/tk/SmartHomeNetworkSim/view/popups/SimulationConfigurator.java

@@ -383,6 +383,7 @@ public class SimulationConfigurator extends JFrame implements Observer{
 				if(mutex)return;
 				try{
 					long l = Long.parseLong(tfStepDuration.getText());
+					if(l<=0)throw new NumberFormatException("Duration shall not be negative");
 					if(!sim.isRunning()){
 						mutex = true;
 						try{