add useful debug info when a file cannot be found..

ui/medashare/btv/__init__.py

@@ -156,15 +156,17 @@ def validate_file(fname, with_file_hashes=None):
 
 	finddname = glob_escape(torrent['info']['name'].decode(_encoding))
 
+	missingfname = None
 	for dirname in fname.parent.rglob(finddname):
 		tordir = dirname.parent
 
 		try:
 			return validate(torrent, tordir, with_file_hashes)
 		except FileNotFoundError as e:
+			missingfname = e.filename
 			continue
 	else:
-		raise FileNotFoundError('unable to find directory for %s' % (repr(fname.name)))
+		raise FileNotFoundError('unable to find directory for %s%s' % (repr(fname.name), (', missing file %s' % repr(missingfname)) if missingfname else ''))
 
 def validate(torrent, basedir, with_file_hashes=None):
 	'''Take a decode torrent file, where it was stored in basedir,