Fix multiple subscription bug on operation filter

A new subscription must be created on every subscribe call, otherwise any
subscribe call after the first directly fails.

Author: Treora

rxjava-core/src/main/java/rx/operators/OperationFilter.java

@@ -37,14 +37,14 @@ private static class Filter<T> implements Func1<Observer<T>, Subscription> {
 
         private final Observable<T> that;
         private final Func1<T, Boolean> predicate;
-        private final AtomicObservableSubscription subscription = new AtomicObservableSubscription();
 
         public Filter(Observable<T> that, Func1<T, Boolean> predicate) {
             this.that = that;
             this.predicate = predicate;
         }
 
         public Subscription call(final Observer<T> observer) {
+            final AtomicObservableSubscription subscription = new AtomicObservableSubscription();
             return subscription.wrap(that.subscribe(new Observer<T>() {
                 public void onNext(T value) {
                     try {