Defensive null check in case Hibernate autoconfig is off

If the Hibernate autoconfig is not used to create an EntityManager
then I suppose it's possible that the JpaProperties might be null
when everything else is ready for the event to be published.

There's no test case because I think it's a corner case.

Fxies gh-1075

Author: Dave Syer

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/orm/jpa/DataSourceInitializedPublisher.java

@@ -73,6 +73,9 @@ && isInitializingDatabase()) {
 	}
 
 	private boolean isInitializingDatabase() {
+		if (this.properties == null) {
+			return true; // better safe than sorry
+		}
 		Map<String, String> hibernate = this.properties
 				.getHibernateProperties(this.dataSource);
 		if (hibernate.containsKey("hibernate.hbm2ddl.auto")) {