plumbing: object: Clamp object timestamps before unix epoch to unix epoch

Signed-off-by: Taru Karttunen <[e-mail]>

plumbing/object/object.go

···
 }
 
 func (s *Signature) encodeTimeAndTimeZone(w io.Writer) error {
-	_, err := fmt.Fprintf(w, "%d %s", s.When.Unix(), s.When.Format("-0700"))
+	u := s.When.Unix()
+	if u < 0 {
+		u = 0
+	}
+	_, err := fmt.Fprintf(w, "%d %s", u, s.When.Format("-0700"))
 	return err
 }
 

plumbing/object/tag_test.go

···
 	c.Assert(tag.String(), Equals,
 		"tag TAG TWO\n"+
 			"Tagger:  <>\n"+
-			"Date:   Mon Jan 01 00:00:00 0001 +0000\n"+
+			"Date:   Thu Jan 01 00:00:00 1970 +0000\n"+
 			"\n"+
 			"tag two\n")
 }