AnimationTrack null checked the animation channel in onStop, onPause and setLoopMode to avoid NPE

git-svn-id: https://jmonkeyengine.googlecode.com/svn/trunk@9288 75d07b2b-3a1a-0410-a2c5-0572b91ccdca

engine/src/core/com/jme3/cinematic/events/AnimationTrack.java

@@ -157,28 +157,32 @@ public class AnimationTrack extends AbstractCinematicEvent {
         }
     }
 
-    
-
     @Override
     public void onUpdate(float tpf) {
     }
 
     @Override
     public void onStop() {
+        if (channel != null) {
             channel.setTime(0);
             channel.reset(false);
         }
+    }
 
     @Override
     public void onPause() {
+        if (channel != null) {
             channel.getControl().setEnabled(false);
         }
+    }
 
     @Override
     public void setLoopMode(LoopMode loopMode) {
         super.setLoopMode(loopMode);
+        if (channel != null) {
             channel.setLoopMode(loopMode);
         }
+    }
 
     @Override
     public void write(JmeExporter ex) throws IOException {