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/Adjust.hs

@@ -38,5 +38,5 @@ seek = commandAction . start
 start :: Adjustment -> CommandStart
 start adj = do
 	checkVersionSupported
-	showStart "adjust" ""
+	showStart' "adjust" Nothing
 	next $ next $ enterAdjustedBranch adj