Fix state entry called too many times

- Fix double entry in a case that target is initial state
  and source is target's direct parent.
- Fixes #191

spring-statemachine-samples/showcase/src/test/java/demo/showcase/ShowcaseTests.java

@@ -82,6 +82,8 @@ public class ShowcaseTests {
 		assertThat(listener.stateChangedLatch.await(1, TimeUnit.SECONDS), is(true));
 		assertThat(listener.stateEnteredLatch.await(1, TimeUnit.SECONDS), is(true));
 		assertThat(listener.stateExitedLatch.await(1, TimeUnit.SECONDS), is(true));
+		assertThat(listener.statesExited.size(), is(2));
+		assertThat(listener.statesEntered.size(), is(2));
 		assertThat(machine.getState().getIds(), contains(States.S0, States.S1, States.S11));
 	}