Minor polish in DispatcherServlet

See gh-23541

spring-webmvc/src/main/java/org/springframework/web/servlet/DispatcherServlet.java

@@ -1131,6 +1131,7 @@ public class DispatcherServlet extends FrameworkServlet {
 		}
 
 		if (mappedHandler != null) {
+			// Exception (if any) is already handled..
 			mappedHandler.triggerAfterCompletion(request, response, null);
 		}
 	}
@@ -1316,7 +1317,7 @@ public class DispatcherServlet extends FrameworkServlet {
 			if (logger.isTraceEnabled()) {
 				logger.trace("Using resolved error view: " + exMv, ex);
 			}
-			if (logger.isDebugEnabled()) {
+			else if (logger.isDebugEnabled()) {
 				logger.debug("Using resolved error view: " + exMv);
 			}
 			WebUtils.exposeErrorRequestAttributes(request, ex, getServletName());

spring-webmvc/src/main/java/org/springframework/web/servlet/HandlerInterceptor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2019 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -141,7 +141,8 @@ public interface HandlerInterceptor {
 	 * @param response current HTTP response
 	 * @param handler handler (or {@link HandlerMethod}) that started asynchronous
 	 * execution, for type and/or instance examination
-	 * @param ex exception thrown on handler execution, if any
+	 * @param ex any exception thrown on handler execution, if any; this does not
+	 * include exceptions that have been handled through an exception resolver
 	 * @throws Exception in case of errors
 	 */
 	default void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler,