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/VCycle.hs

@@ -27,7 +27,7 @@ start = go =<< currentView
   where
 	go Nothing = giveup "Not in a view."
 	go (Just v) = do
-		showStart "vcycle" ""
+		showStart' "vcycle" Nothing
 		let v' = v { viewComponents = vcycle [] (viewComponents v) }
 		if v == v'
 			then do