importfeed: Avoid using youtube-dl when a feed does not contain an enclosure, but only a link to an url which youtube-dl does not support

This is common in some feeds, which might mix some items with enclosures,
with others that link to posts or whatever. Before this, it would try to
use youtube-dl and fail, or if youtube-dl was not allowed, it would
incorrectly complain that an url was supported by youtube-dl.

CHANGELOG

@@ -20,6 +20,8 @@ git-annex (8.20201128) UNRELEASED; urgency=medium
   * Fix reversion in 8.20201116 that made include= and exclude= in
     preferred/required content expressions match a path relative to the
     current directory, rather than the path from the top of the repository.
+  * importfeed: Avoid using youtube-dl when a feed does not contain an
+    enclosure, but only a link to an url which youtube-dl does not support.
 
  -- Joey Hess <id@joeyh.name>  Mon, 30 Nov 2020 12:55:49 -0400
 

Command/ImportFeed.hs

@@ -308,7 +308,8 @@ performDownload addunlockedmatcher opts cache todownload = case location todownl
 	
 	downloadmedia linkurl mediaurl mediakey
 		| rawOption (downloadOptions opts) = downloadlink
-		| otherwise = do
+		| otherwise = ifM (youtubeDlSupported linkurl)
+			( do
 				r <- withTmpWorkDir mediakey $ \workdir -> do
 					dl <- youtubeDl linkurl (fromRawFilePath workdir) nullMeterUpdate
 					case dl of
@@ -321,14 +322,16 @@ performDownload addunlockedmatcher opts cache todownload = case location todownl
 									addWorkTree canadd addunlockedmatcher webUUID mediaurl f mediakey (Just (toRawFilePath mediafile))
 									return (Just [mediakey])
 							return (Just ok)
-					-- youtude-dl didn't support it, so
+						-- youtube-dl didn't support it, so
 						-- download it as if the link were
 						-- an enclosure.
 						Right Nothing -> Just <$> downloadlink
 						Left msg -> do
-						warning msg
+							warning $ linkurl ++ ": " ++ msg
 							return Nothing
 				return (fromMaybe False r)
+			, downloadlink
+			)
 	  where
 		downloadlink = performDownload addunlockedmatcher opts cache todownload
 			{ location = Enclosure linkurl }