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/Whereis.hs

@@ -53,7 +53,7 @@ start remotemap file key = startKeys remotemap key (mkActionItem afile)
 
 startKeys :: M.Map UUID Remote -> Key -> ActionItem -> CommandStart
 startKeys remotemap key ai = do
-	showStart' "whereis" key ai
+	showStartKey "whereis" key ai
 	next $ perform remotemap key
 
 perform :: M.Map UUID Remote -> Key -> CommandPerform