Activate item tab only when inactive, fixes tab reset on select value change
Makes sure that the tab is not already active when render() checks for the activate flag. This delays re-activation until after the item dialog is recreated, so that the tab is properly selected after a change is made to a select or text input.
In the future, maybe the tab can be integrated more directly into the item dialog rendering so that it isn't lost on a re-render and doesn't have to be patched in like this.