MM-21481: Fixed several issues from user marshalling (#13627)

* MM-21481: Fixed several issues from user marshalling

- Fixed the root cause for panic by properly converting
the map to a User struct.
- Added a check for type conversion for extra safety.
- Fixed a somewhat unrelated issue of a pointer to pointer reference.

* Fix tests

app/user.go

@@ -1111,7 +1111,7 @@ func (a *App) sendUpdatedUserEvent(user model.User) {
 	adminCopyOfUser := user.DeepCopy()
 	a.SanitizeProfile(adminCopyOfUser, true)
 	adminMessage := model.NewWebSocketEvent(model.WEBSOCKET_EVENT_USER_UPDATED, "", "", "", nil)
-	adminMessage.Add("user", &adminCopyOfUser)
+	adminMessage.Add("user", adminCopyOfUser)
 	adminMessage.GetBroadcast().ContainsSensitiveData = true
 	a.Publish(adminMessage)