Prevent NPE in RemoteStore:stop

Caused by: org.infinispan.commons.CacheConfigurationException: Failed to construct component org.infinispan.executors.non-blocking, path org.infinispan.executors.non-blocking << org.infinispan.util.concurrent.BlockingManager (a org.infinispan.util.concurrent.BlockingManagerImpl) << org.infinispan.notifications.cachemanagerlistener.CacheManagerNotifier (a org.infinispan.notifications.cachemanagerlistener.CacheManagerNotifierImpl) at org.infinispan.factories.impl.BasicComponentRegistryImpl.doInstantiateWrapper(BasicComponentRegistryImpl.java:192) [ERROR] org.infinispan.persistence.remote.RemoteStoreTest.persistence.remote.RemoteStoreTest Time elapsed: 36.777 s <<< FAILURE! java.lang.NullPointerException at org.infinispan.persistence.remote.RemoteStore.stop(RemoteStore.java:205) at org.infinispan.persistence.support.EnsureNonBlockingStore.lambda$stop$1(EnsureNonBlockingStore.java:31)