Fix ResourceHttpRequestHandler delegate

Fix ResourceHttpRequestHandler to set the ServletContext following the
Spring Framework update for SPR-14851.

Author: philwebb

spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/mvc/LogFileMvcEndpoint.java

@@ -19,6 +19,7 @@
 import java.io.File;
 import java.io.IOException;
 
+import javax.servlet.ServletContext;
 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
@@ -82,7 +83,8 @@ public void invoke(HttpServletRequest request, HttpServletResponse response)
 			}
 			resource = null;
 		}
-		new Handler(resource).handleRequest(request, response);
+		Handler handler = new Handler(resource, request.getServletContext());
+		handler.handleRequest(request, response);
 	}
 
 	private Resource getLogFileResource() {
@@ -104,10 +106,11 @@ private static class Handler extends ResourceHttpRequestHandler {
 
 		private final Resource resource;
 
-		Handler(Resource resource) {
+		Handler(Resource resource, ServletContext servletContext) {
 			this.resource = resource;
 			getLocations().add(resource);
 			try {
+				setServletContext(servletContext);
 				afterPropertiesSet();
 			}
 			catch (Exception ex) {