download: handle binary file misdetected as html

[myfreeer]

This mean resources with its type ResourceType.Html, but the content type is available and being not html, very possible being an image or binary file.
Since the resource referencing this file could be already saved to disk, and there is no reference map that can tell that which resources referenced this file, so it's hard to deal with such kind of files, but at least we can make a warning log so users can fix in their detectResourceType life cycle.