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/Get.hs

@@ -71,7 +71,7 @@ start' expensivecheck from key afile ai = onlyActionOn key $
 					go $ Command.Move.fromPerform src False key afile
   where
 	go a = do
-		showStart' "get" key ai
+		showStartKey "get" key ai
 		next a
 
 perform :: Key -> AssociatedFile -> CommandPerform