Do not launch comparison dialog if live PV is not connected

Author: georgweiss

app/save-and-restore/app/src/main/java/org/phoebus/applications/saveandrestore/ui/snapshot/VDeltaCellEditor.java

@@ -96,6 +96,8 @@ public void updateItem(T item, boolean empty) {
                             comparisonDialog.show();
                         });
                     } else {
+                        // Do not handle mouse clicked, e.g. if live PV is disconnected.
+                        setOnMouseClicked(e -> {});
                         String percentage = Utilities.deltaValueToPercentage(pair.value, pair.base);
                         if (!percentage.isEmpty() && showDeltaPercentage) {
                             Formatter formatter = new Formatter();