Refine check

Refine commit 8a96481 to set the web environment to false if spring web
is not available in the classpath. Thanks to @mjustin for spotting that
mistake.

Closes gh-3856

spring-boot/src/main/java/org/springframework/boot/SpringApplication.java

@@ -864,7 +864,7 @@ public class SpringApplication {
 	public void setApplicationContextClass(
 			Class<? extends ConfigurableApplicationContext> applicationContextClass) {
 		this.applicationContextClass = applicationContextClass;
-		if (isSpringWebAvailable() && !WebApplicationContext.class.isAssignableFrom(
+		if (!isSpringWebAvailable() || !WebApplicationContext.class.isAssignableFrom(
 				applicationContextClass)) {
 			this.webEnvironment = false;
 		}