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/Fsck.hs

@@ -536,7 +536,7 @@ badContentRemote remote localcopy key = do
 runFsck :: Incremental -> ActionItem -> Key -> Annex Bool -> CommandStart
 runFsck inc ai key a = ifM (needFsck inc key)
 	( do
-		showStart' "fsck" key ai
+		showStartKey "fsck" key ai
 		next $ do
 			ok <- a
 			when ok $