Check Request-Level Servlet Context First

Because test do not always attach a fully-formulated ServletContext
to the mock request, it's beneficial to consult the ServletContext
presented during application startup.

In case the request does have needed material, though, it maybe
be helpful for Spring Security to first consult the request.

Issue spring-projectsgh-14418

config/src/main/java/org/springframework/security/config/annotation/web/AbstractRequestMatcherRegistry.java

@@ -529,7 +529,7 @@ static class DispatcherServletDelegatingRequestMatcher implements RequestMatcher
 		@Override
 		public boolean matches(HttpServletRequest request) {
 			String name = request.getHttpServletMapping().getServletName();
-			ServletRegistration registration = this.servletContext.getServletRegistration(name);
+			ServletRegistration registration = servletRegistration(request, name);
 			Assert.notNull(registration, "Failed to find servlet [" + name + "] in the servlet context");
 			if (isDispatcherServlet(registration)) {
 				return this.mvc.matches(request);
@@ -540,14 +540,22 @@ public boolean matches(HttpServletRequest request) {
 		@Override
 		public MatchResult matcher(HttpServletRequest request) {
 			String name = request.getHttpServletMapping().getServletName();
-			ServletRegistration registration = this.servletContext.getServletRegistration(name);
+			ServletRegistration registration = servletRegistration(request, name);
 			Assert.notNull(registration, "Failed to find servlet [" + name + "] in the servlet context");
 			if (isDispatcherServlet(registration)) {
 				return this.mvc.matcher(request);
 			}
 			return this.ant.matcher(request);
 		}
 
+		private ServletRegistration servletRegistration(HttpServletRequest request, String name) {
+			ServletRegistration registration = request.getServletContext().getServletRegistration(name);
+			if (registration != null) {
+				return registration;
+			}
+			return this.servletContext.getServletRegistration(name);
+		}
+
 		private boolean isDispatcherServlet(ServletRegistration registration) {
 			Class<?> dispatcherServlet = ClassUtils
 				.resolveClassName("org.springframework.web.servlet.DispatcherServlet", null);