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

Author: lunny

models/org.go

@@ -275,10 +275,12 @@ func deleteOrg(e *xorm.Session, u *User) error {
 		return fmt.Errorf("Failed to RemoveAll %s: %v", path, err)
 	}
 
-	avatarPath := u.CustomAvatarPath()
-	if com.IsExist(avatarPath) {
-		if err := os.Remove(avatarPath); err != nil {
-			return fmt.Errorf("Failed to remove %s: %v", avatarPath, 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)
+			}
 		}
 	}