Undeclared variable in AttributeGroupsController.php

It looks like this has been in since initial commit.

On line 51 of app/src/Controller/AttributeGroupsController.php, a Notice-level message is thrown 'Undefined Property AttributeGroupsController::$mgid'

I worked around by copying matching code from another controller:

49+ $mgid = isset($this->cur_mg->id) ? $this->cur_mg->id : null;

51 $platformAdmin = $this->Authorization->isPlatformAdmin($user['username']);

53-  $mgAdmin = $this->Authorization->isMatchAdmin($user['username'], $this->mgid);

53+ $mgAdmin = $this->Authorization->isMatchAdmin($user['username'], $mgid);