metadata: Fix broken retrieval for screenshots

Test could never have been evaluated to true
metadata: fix stray declaration
metadata: Fix GetGrabber

It would never have used the grabber set in the inetref
metadata: also set collectionref to new format
metadata: no need to re-run the search when a match has already been found
metadata: properly handle media search type if we already have an extended inetref.
metadata: allow nfo and mxml in DVD/BD rip directory
remotefile: Use more accurate MythCoreContext::IsThisHost(host) API