ignore IllegalStateException when removing shutdown hook (SPR-6793)

org.springframework.context/src/main/java/org/springframework/context/support/AbstractApplicationContext.java

@@ -944,7 +944,12 @@ public abstract class AbstractApplicationContext extends DefaultResourceLoader
 			// If we registered a JVM shutdown hook, we don't need it anymore now:
 			// We've already explicitly closed the context.
 			if (this.shutdownHook != null) {
-				Runtime.getRuntime().removeShutdownHook(this.shutdownHook);
+				try {
+					Runtime.getRuntime().removeShutdownHook(this.shutdownHook);
+				}
+				catch (IllegalStateException ex) {
+					// ignore - VM is already shutting down
+				}
 			}
 		}
 	}