Scheduler.isDisposed() only true for disposed instances (#3243)

Some schedulers for optimization purposes started in a state
which was considered as disposed (Scheduler#isDisposed()).
This change affects only BoundedElasticScheduler as it was
the last one which behaved this way.
This is a change of behavior, however one which was not documented.

reactor-core/src/main/java/reactor/core/scheduler/BoundedElasticScheduler.java

@@ -144,7 +144,9 @@ BoundedScheduledExecutorService createBoundedExecutorService() {
 
 	@Override
 	public boolean isDisposed() {
-		return state.currentResource == SHUTDOWN;
+		// we only consider disposed as actually shutdown
+		SchedulerState<BoundedServices> current = this.state;
+		return current != INIT && current.currentResource == SHUTDOWN;
 	}
 
 	@Override

reactor-core/src/test/java/reactor/core/scheduler/AbstractSchedulerTest.java

@@ -110,7 +110,6 @@ protected boolean isTerminated(Scheduler s) {
 	}
 
 	@Test
-	@Disabled("Should be enabled in 3.5.0")
 	void nonInitializedIsNotDisposed() {
 		Scheduler s = freshScheduler();
 		assertThat(s.isDisposed()).isFalse();