Async Mode error "flush your menu cache" when using s3fs module

I think I've found the cause of the Async Mode error being displayed. The problem is in the advagg.install file when running the s3fs module. Each time the AdvAgg pages are loaded, the following error message is shown:

Adv CSS/JS Agg - Async Mode	Flush your caches.
You need to flush your menu cache. This can be done at the top of the performance page; under "Clear cache" press the "Clear all caches" button.

No matter how many times the cache is flushed, the error still occurs.

The cause of the issue is how the $css_path and $js_path arrays are used in the advagg_install_fast_checks function. In the block of code to check that the menu router handler is working, it first checks if $css_path[1] and $js_path[1] are not uris. By default, it seems as though these values could never be uris -- they are "advagg_css" and "advagg_js" respectively. (The uris exist in the 0 value of the array, for example, $css_path[0] = "public://advagg_css".)

The problem occurs on the next line where menu_get_item is run. This will never work when using S3, because "advagg_js/test.js" is always going to return an empty result. Based on how the code works, I can't see a situation where this code would not display an error.

The attached patch wraps the code in a !module_exists('s3fs') so that it is skipped if s3fs is present.

Let me know if there is a better way to handle this or something I might be missing. Thanks.