Break OnDestroy at setOnModelChange

[mqi-diamonddiagnostics-com]

Hi I believe this is rarely witnessed but it is better to be logically fixed.
Here is the scenario:
A component with currencyMask on a form control is defined and is being rendered. Before the GUI finished rendering, immediately, you destroy this component, by router change for example. An TypeError for reading 'setOnModelChange' will be thrown.
This is because Angular clean up control before destroying the component and any controls with valueAccessor will call registerOnChange and registerOnTouch during this cleanup procedure.
In our registerOnChange and registerOnTouch function, we call setOnModelChange directly from the handler, which is created in ngOnInit. So in the scenario above, the handler was not created yet and the registerOnChange is called.
I suggest to use this._handler?.setOnModelChange instead, so it is safer.
ngx-currency.directive.ts