git: Add commit validation for Reset. Fixes go-git#878

Signed-off-by: Paulo Gomes <paulo.gomes@suse.com>

options.go

@@ -408,6 +408,11 @@ func (o *ResetOptions) Validate(r *Repository) error {
 		}
 
 		o.Commit = ref.Hash()
+	} else {
+		_, err := r.CommitObject(o.Commit)
+		if err != nil {
+			return fmt.Errorf("invalid reset option: %w", err)
+		}
 	}
 
 	return nil

options_test.go

@@ -23,6 +23,12 @@ func (s *OptionsSuite) TestCommitOptionsParentsFromHEAD(c *C) {
 	c.Assert(o.Parents, HasLen, 1)
 }
 
+func (s *OptionsSuite) TestResetOptionsCommitNotFound(c *C) {
+	o := ResetOptions{Commit: plumbing.NewHash("ab1b15c6f6487b4db16f10d8ec69bb8bf91dcabd")}
+	err := o.Validate(s.Repository)
+	c.Assert(err, NotNil)
+}
+
 func (s *OptionsSuite) TestCommitOptionsCommitter(c *C) {
 	sig := &object.Signature{}