Resolves: fdo#69645 Parent Node disposed and mpParent pointing to junk

mpParent points the contents of mxParent which is a WeakReference, so
we can check if the WeakReference is still valid before using mpParent

Change-Id: I40424714865e506b8cf27017539795eb834e10d2

animations/source/animcore/animcore.cxx

@@ -2060,7 +2060,8 @@ void AnimationNode::fireChangeListener()
         }
     }
 
-    if( mpParent )
+    //fdo#69645 use get() on WeakReference of mxParent to test if mpParent is still valid
+    if( mpParent && mxParent.get().is() )
         mpParent->fireChangeListener();
 }