Don't generate a CTL (EU) counterexample (witness) when the property is false.

git-svn-id: https://www.prismmodelchecker.org/svn/prism/prism/trunk@3178 bbc10eb1-c90d-0410-af57-cb519fbb1720

prism/src/prism/NonProbModelChecker.java

@@ -264,6 +264,11 @@ public class NonProbModelChecker extends StateModelChecker
 
 		// Process the counterexample info to produce a trace 
 		if (doGenCex) {
+			if (!cexDone) {
+				for (i = 0; i < cexDDs.size(); i++) {
+					JDD.Deref(cexDDs.get(i));
+				}
+			} else {
 				mainLog.println("\nProcessing counterexample trace (length " + (cexDDs.size() - 1) + ")...");
 				// First state of counterexample (at end of array) is initial state
 				JDD.Deref(cexDDs.get(cexDDs.size() - 1));
@@ -317,6 +322,7 @@ public class NonProbModelChecker extends StateModelChecker
 					result.setCounterexample(cex);
 				}
 			}
+		}
 
 		l = System.currentTimeMillis() - l;