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/TestRemote.hs

@@ -58,7 +58,7 @@ seek o = commandAction $ start (fromInteger $ sizeOption o) (testRemote o)
 
 start :: Int -> RemoteName -> CommandStart
 start basesz name = do
-	showStart "testremote" name
+	showStart' "testremote" (Just name)
 	fast <- Annex.getState Annex.fast
 	r <- either giveup disableExportTree =<< Remote.byName' name
 	rs <- catMaybes <$> mapM (adjustChunkSize r) (chunkSizes basesz fast)