Fix JSP availability check when not running as a packaged war

See gh-12859

Author: Mandap

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/JspTemplateAvailabilityProvider.java

@@ -38,7 +38,8 @@ public boolean isTemplateAvailable(String view, Environment environment,
 			ClassLoader classLoader, ResourceLoader resourceLoader) {
 		if (ClassUtils.isPresent("org.apache.jasper.compiler.JspConfig", classLoader)) {
 			String resourceName = getResourceName(view, environment);
-			return resourceLoader.getResource(resourceName).exists();
+			return resourceLoader.getResource(resourceName).exists() ||
+					resourceLoader.getResource("file:./src/main/webapp" + resourceName).exists();
 		}
 		return false;
 	}