checkout: fix dirty-file display.

When we refused to switch branches, we incorrectly showed
differences from the branch we would have switched to.

Signed-off-by: Junio C Hamano <junkio@cox.net>

git-checkout.sh

@@ -165,8 +165,10 @@ else
 	exit 0
     )
     saved_err=$?
-    test "$new" = "$old" ||
-	git diff-index --name-status "$new"
+    if test "$saved_err" = 0
+    then
+	test "$new" = "$old" || git diff-index --name-status "$new"
+    fi
     (exit $saved_err)
 fi