fix del org avatar potential delete all avtars (#1120)

models/org.go

@@ -275,12 +275,14 @@ func deleteOrg(e *xorm.Session, u *User) error {
 		return fmt.Errorf("Failed to RemoveAll %s: %v", path, err)
 	}
 
+	if len(u.Avatar) > 0 {
 		avatarPath := u.CustomAvatarPath()
 		if com.IsExist(avatarPath) {
 			if err := os.Remove(avatarPath); err != nil {
 				return fmt.Errorf("Failed to remove %s: %v", avatarPath, err)
 			}
 		}
+	}
 
 	return nil
 }