Make sure only one user exists with a particular email when updating

pkg/user/user.go

@@ -335,6 +335,19 @@ func UpdateUser(user *User) (updatedUser *User, err error) {
 		}
 	}
 
+	// Check if the email is already used
+	if user.Email == "" {
+		user.Email = theUser.Email
+	} else {
+		uu, err := getUser(&User{Email: user.Email}, true)
+		if err != nil && !IsErrUserDoesNotExist(err) {
+			return nil, err
+		}
+		if uu.ID != user.ID {
+			return nil, &ErrUserEmailExists{Email: user.Email, UserID: uu.ID}
+		}
+	}
+
 	user.Password = theUser.Password // set the password to the one in the database to not accedently resetting it
 
 	// Validate the avatar type