Mdl dialog create 2 mdl-backdrop-overlay's

[maximelkin]

This leads to bug with closing dialog (page is still clickable and blurred)

[maximelkin]

This bug reproducing on dialog-outlet placed inside app-root
MdlDialogInnerOutletComponent constructor -> setDefaultViewContainerRef -> setViewContainerRef -> created MdlBackdropOverlayComponent

And

MdlDialogOutletService constructor -> ngZone.onStable.pipe subscribe -> setViewContainerRef -> created MdlBackdropOverlayComponent

So this 2 flows creates 2 MdlBackdropOverlayComponent

[maximelkin]

Temporary workaround

const initial = (MdlDialogOutletService.prototype as any).setViewContainerRef;
(MdlDialogOutletService.prototype as any).setViewContainerRef = function(...args) {
    if (!this.backdropComponent) {
        initial.apply(this, args);
    }
};