display destination file before youtube-dl download

Rather than after it, which can leave one wondering what file it's
downloading.

youtubeDl should not ever return Right Nothing in normal operation,
becaause it's already asked youtube-dl if it supports the url. So it
would have to succeed at that, then not download any file, but also
exit successfully, in order for the new error message to display.

Also display the name of yt-dlp when using it.

Command/AddUrl.hs

@@ -353,21 +353,25 @@ downloadWeb addunlockedmatcher o url urlinfo file =
 	  where
 		dl dest = withTmpWorkDir mediakey $ \workdir -> do
 			let cleanuptmp = pruneTmpWorkDirBefore tmp (liftIO . removeWhenExistsWith R.removeLink)
-			showNote "using youtube-dl"
+			dlcmd <- youtubeDlCommand
+			showNote ("using " <> UnquotedString dlcmd)
 			Transfer.notifyTransfer Transfer.Download url $
-				Transfer.download' webUUID mediakey (AssociatedFile Nothing) Nothing Transfer.noRetry $ \p ->
+				Transfer.download' webUUID mediakey (AssociatedFile Nothing) Nothing Transfer.noRetry $ \p -> do
+					showDestinationFile dest
 					youtubeDl url (fromRawFilePath workdir) p >>= \case
 						Right (Just mediafile) -> do
 							cleanuptmp
 							checkCanAdd o dest $ \canadd -> do
-								showDestinationFile dest
 								addWorkTree canadd addunlockedmatcher webUUID mediaurl dest mediakey (Just (toRawFilePath mediafile))
 								return $ Just mediakey
-						Right Nothing -> checkRaw Nothing o (pure Nothing) (normalfinish tmp backend)
 						Left msg -> do
 							cleanuptmp
 							warning (UnquotedString msg)
 							return Nothing
+						Right Nothing -> do
+							cleanuptmp
+							warning (UnquotedString dlcmd <> " did not download anything")
+							return Nothing
 		mediaurl = setDownloader url YoutubeDownloader
 		mediakey = Backend.URL.fromUrl mediaurl Nothing
 		-- Does the already annexed file have the mediaurl