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/FromKey.hs

@@ -41,7 +41,7 @@ start force (keyname, file) = do
 
 startMass :: CommandStart
 startMass = do
-	showStart "fromkey" "stdin"
+	showStart' "fromkey" (Just "stdin")
 	next massAdd
 
 massAdd :: CommandPerform