add null check for avoid npe

Author: jschneider

src/main/java/io/reactivex/internal/schedulers/NewThreadWorker.java

@@ -127,7 +127,9 @@ public ScheduledRunnable scheduleActual(final Runnable run, long delayTime, Time
             }
             sr.setFuture(f);
         } catch (RejectedExecutionException ex) {
-            parent.remove(sr);
+            if (parent != null) {
+                parent.remove(sr);
+            }
             RxJavaPlugins.onError(ex);
         }