GUI bug fix: null pointer when graph dialog closed.

git-svn-id: https://www.prismmodelchecker.org/svn/prism/prism/trunk@764 bbc10eb1-c90d-0410-af57-cb519fbb1720

prism/src/userinterface/properties/GUIGraphPicker.java

@@ -87,8 +87,11 @@ public class GUIGraphPicker extends javax.swing.JDialog
         this.experiment = experiment;
         this.graphHandler = graphHandler;        
         this.resultsCollection = experiment.getResults();        
-                
-        this.graphCancelled = false;
+        
+        // graphCancelled will be set explictly to false when the OK button is pressed
+        // (this means if the user closes the dialog, this counts as a cancel)
+        this.graphCancelled = true;
+        
         this.multiSeries = new Vector<DefinedConstant>();
        
         initComponents();