Only wait for background preinit to complete when it has started

Closes gh-10362

Author: wilkinsona

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/BackgroundPreinitializer.java

@@ -46,7 +46,8 @@
 public class BackgroundPreinitializer
 		implements ApplicationListener<SpringApplicationEvent> {
 
-	private static final AtomicBoolean preinitializationStarted = new AtomicBoolean(false);
+	private static final AtomicBoolean preinitializationStarted = new AtomicBoolean(
+			false);
 
 	private static final CountDownLatch preinitializationComplete = new CountDownLatch(1);
 
@@ -57,8 +58,9 @@ public void onApplicationEvent(SpringApplicationEvent event) {
 				performPreinitialization();
 			}
 		}
-		if (event instanceof ApplicationReadyEvent
-				|| event instanceof ApplicationFailedEvent) {
+		if ((event instanceof ApplicationReadyEvent
+				|| event instanceof ApplicationFailedEvent)
+				&& preinitializationStarted.get()) {
 			try {
 				preinitializationComplete.await();
 			}