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/MetaData.hs

@@ -100,7 +100,7 @@ startKeys c o k ai = case getSet o of
 			putStrLn . fromMetaValue
 		stop
 	_ -> do
-		showStart' "metadata" k ai
+		showStartKey "metadata" k ai
 		next $ perform c o k
 
 perform :: VectorClock -> MetaDataOptions -> Key -> CommandPerform
@@ -164,7 +164,7 @@ startBatch (i, (MetaData m)) = case i of
 	Right k -> go k (mkActionItem k)
   where
 	go k ai = do
-		showStart' "metadata" k ai
+		showStartKey "metadata" k ai
 		let o = MetaDataOptions
 			{ forFiles = []
 			, getSet = if MetaData m == emptyMetaData