No Null Guard in _removeContainer

[thkruz]

Double clicking a toast message results in an error due to container being null and trying to fire .remove().

materialize/components/snackbar/toasts.ts

Lines 125 to 130 in 0f4376b

	static _removeContainer() {
	document.removeEventListener('mousemove', Toast._onDragMove);
	document.removeEventListener('mouseup', Toast._onDragEnd);
	Toast._container.remove();
	Toast._container = null;
	}

Adding a simple null guard would resolve this issue. Happy to do the PR if I can get a confirmation that it isn't something unique I am doing. I suspect that these kind of errors go unnoticed for a lot of people but is triggering my telemetry that watches for any errors globaly.