fix error when there is no power plant on canvas

src/algo/TestAlgo.java

@@ -242,6 +242,10 @@ public class TestAlgo implements AddOn {
 			renewableProducers = getRenewableProducers();
 			consumers = getConsumers();
 			powerPlant = getPowerPlant();// DANGER DONT GIVE NULL
+			if(powerPlant == null){
+				println("No Power Plant in Model");
+				return;
+			}
 			calcResistance();
 			blackstartRunningCounter = 0;
 			deactivateBlackstart();