Ensure lfs check within transaction

The previous code made it possible for a race condition to occur whereby a LFSMetaObject could be checked into the database twice. We should check if the LFSMetaObject is within the database and insert it if not in one transaction.

models/lfs.go

@@ -44,20 +44,20 @@ const (
 func NewLFSMetaObject(m *LFSMetaObject) (*LFSMetaObject, error) {
 	var err error
 
-	has, err := x.Get(m)
+	sess := x.NewSession()
+	defer sess.Close()
+	if err = sess.Begin(); err != nil {
+		return nil, err
+	}
+
+	has, err := sess.Get(m)
 	if err != nil {
 		return nil, err
 	}
 
 	if has {
 		m.Existing = true
-		return m, nil
-	}
-
-	sess := x.NewSession()
-	defer sess.Close()
-	if err = sess.Begin(); err != nil {
-		return nil, err
+		return m, sess.Commit()
 	}
 
 	if _, err = sess.Insert(m); err != nil {