showStart variant for when there's no worktree file

Clean up some uses of showStart with "" for the file,
or in some cases, a non-filename description string. That would
generate bad json, although none of the commands doing that
supported --json.

Using "" for the file resulted in output like "foo  rest";
now the extra space is eliminated.

This commit was sponsored by Fernando Jimenez on Patreon.

Command/Multicast.hs

@@ -78,7 +78,7 @@ seek (MultiCastOptions Receive _ _) = giveup "Cannot specify list of files with
 
 genAddress :: CommandStart
 genAddress = do
-	showStart "gen-address" ""
+	showStart' "gen-address" Nothing
 	k <- uftpKey
 	(s, ok) <- case k of
 		KeyContainer s -> liftIO $ genkey (Param s)
@@ -130,7 +130,7 @@ send ups fs = withTmpFile "send" $ \t h -> do
 	whenM isDirect $
 		giveup "Sorry, multicast send cannot be done from a direct mode repository."
 	
-	showStart "generating file list" ""
+	showStart' "generating file list" Nothing
 	fs' <- seekHelper LsFiles.inRepo =<< workTreeItems fs
 	matcher <- Limit.getMatcher
 	let addlist f o = whenM (matcher $ MatchingFile $ FileInfo f f) $
@@ -143,7 +143,7 @@ send ups fs = withTmpFile "send" $ \t h -> do
 	liftIO $ hClose h
 	showEndOk
 
-	showStart "sending files" ""
+	showStart' "sending files" Nothing
 	showOutput
 	serverkey <- uftpKey
 	u <- getUUID
@@ -169,7 +169,7 @@ send ups fs = withTmpFile "send" $ \t h -> do
 
 receive :: [CommandParam] -> CommandStart
 receive ups = do
-	showStart "receiving multicast files" ""
+	showStart' "receiving multicast files" Nothing
 	showNote "Will continue to run until stopped by ctrl-c"
 	
 	showOutput