MM-56881 Validate and ensure valid CustomStatus is stored (#26287)

* don't allow invalid CustomStatus

* allow empty emoji in custom status

* lint fix

* add english translation

* update for review comments.

* fix bad fix

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/public/model/user.go

@@ -399,6 +399,13 @@ func (u *User) IsValid() *AppError {
 			map[string]any{"Limit": UserRolesMaxLength}, "user_id="+u.Id+" roles_limit="+u.Roles, http.StatusBadRequest)
 	}
 
+	if u.Props != nil {
+		if !u.ValidateCustomStatus() {
+			return NewAppError("User.IsValid", "model.user.is_valid.invalidProperty.app_error",
+				map[string]any{"Props": u.Props}, "user_id="+u.Id, http.StatusBadRequest)
+		}
+	}
+
 	return nil
 }
 
@@ -472,6 +479,12 @@ func (u *User) PreSave() {
 	if u.Password != "" {
 		u.Password = HashPassword(u.Password)
 	}
+
+	cs := u.GetCustomStatus()
+	if cs != nil {
+		cs.PreSave()
+		u.SetCustomStatus(cs)
+	}
 }
 
 // PreUpdate should be run before updating the user in the db.
@@ -508,6 +521,14 @@ func (u *User) PreUpdate() {
 		}
 		u.NotifyProps[MentionKeysNotifyProp] = strings.Join(goodKeys, ",")
 	}
+
+	if u.Props != nil {
+		cs := u.GetCustomStatus()
+		if cs != nil {
+			cs.PreSave()
+			u.SetCustomStatus(cs)
+		}
+	}
 }
 
 func (u *User) SetDefaultNotifications() {
@@ -711,6 +732,17 @@ func (u *User) ClearCustomStatus() {
 	u.Props[UserPropsKeyCustomStatus] = ""
 }
 
+func (u *User) ValidateCustomStatus() bool {
+	status, exists := u.Props[UserPropsKeyCustomStatus]
+	if exists && status != "" {
+		cs := u.GetCustomStatus()
+		if cs == nil {
+			return false
+		}
+	}
+	return true
+}
+
 func (u *User) GetFullName() string {
 	if u.FirstName != "" && u.LastName != "" {
 		return u.FirstName + " " + u.LastName