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/Schedule.hs

@@ -28,7 +28,7 @@ start = parse
 	parse (name:[]) = go name performGet
 	parse (name:expr:[]) = go name $ \uuid -> do
 		allowMessages
-		showStart "schedule" name
+		showStart' "schedule" (Just name)
 		performSet expr uuid
 	parse _ = giveup "Specify a repository."