Compatibility with org.springframework.web.servlet.view.ContentNegotiatingViewResolver

This pull request has been made to be able to chain the ViewResolvers (as previously intended by Spring).

The pull request includes:

A overridden method checkResource() returning false when no template is attached to the view.
A test case for avoiding regressions.

Tested on an application using both the Mustache templating and Freemarker templating. Works fine. The development follows the FreemarkerViewResolver.

sps / mustache-spring-view

Compatibility with org.springframework.web.servlet.view.ContentNegotiatingViewResolver #17