Fixed Default avatar URL for Gravatar broken when using custom imagePath

When using a customized URL for imagePath in a style the default avatar URL that gets passed to Gravatar is broken.

With default setting the (unescaped) URL is in the form of

When switching imagePath to a CDN (e.g. the default avatar URL becomes

As long as the user has a working Gravatar, everything is OK. However if a Gravatar is set, but Gravatar reverts to the default, we get a broken image. Gravatar does a 302 redirect to

Running XenForo v1.3.3 with no add-ons enabled and using the default style.