Prevent NPE.

Change-Id: I622ab898d0875793d5220d3f78844464ab162356
Signed-off-by: Ali Akar <ali.akar82@gmail.com>
diff --git a/plugins/org.eclipse.amalgam.explorer.activity.ui/src/org/eclipse/amalgam/explorer/activity/ui/internal/session/listeners/ActivityExplorerSessionListener.java b/plugins/org.eclipse.amalgam.explorer.activity.ui/src/org/eclipse/amalgam/explorer/activity/ui/internal/session/listeners/ActivityExplorerSessionListener.java
index 0ed9582..0253c76 100644
--- a/plugins/org.eclipse.amalgam.explorer.activity.ui/src/org/eclipse/amalgam/explorer/activity/ui/internal/session/listeners/ActivityExplorerSessionListener.java
+++ b/plugins/org.eclipse.amalgam.explorer.activity.ui/src/org/eclipse/amalgam/explorer/activity/ui/internal/session/listeners/ActivityExplorerSessionListener.java
@@ -158,16 +158,12 @@
 
   @Override
   public void viewpointSelected(Viewpoint selectedViewpoint) {
-    if (session.isOpen()) {
       update(selectedViewpoint);
-    }
   }
 
   @Override
   public void viewpointDeselected(Viewpoint deselectedViewpoint) {
-    if (session.isOpen()) {
       update(deselectedViewpoint);
-    }
   }
 
 	/**
@@ -176,7 +172,7 @@
 	 * @param selectedViewpoint
 	 */
 	private void update(Viewpoint selectedViewpoint) {
-		if (selectedViewpoint != null && session != null) {
+		if (selectedViewpoint != null && session != null && session.isOpen()) {
 
 			Runnable refresh = new Runnable() {