MM_22682_Centralize_ID_Validation (#14237)

Co-authored-by: mattermod <mattermod@users.noreply.github.com>

model/user.go

@@ -237,7 +237,7 @@ func (u *User) DeepCopy() *User {
 // correctly.
 func (u *User) IsValid() *AppError {
 
-	if len(u.Id) != 26 {
+	if !IsValidId(u.Id) {
 		return InvalidUserError("id", "")
 	}