WebXRManager throws error in onSessionEnd if getController is never called

[kalegd]

TLDR: Lack of null check for controllers in onSessionEnd causes errors if getController is never called

It seems controllers are only created when getController or getControllerGrip are called. if those functions are never called, we end up with null controllers in the inputSourcesMap

three.js/src/renderers/webxr/WebXRManager.js

Lines 337 to 344 in 1238a32

	// Assign controllers to available inputSources
	for ( let i = 0; i < inputSources.length; i ++ ) {
	const index = inputSources[ i ].handedness === 'right' ? 1 : 0;
	inputSourcesMap.set( inputSources[ i ], controllers[ index ] );
	}

Once the session ends, there's no null check for the controllers when trying to disconnect them as seen below

three.js/src/renderers/webxr/WebXRManager.js

Lines 132 to 138 in 1238a32

	function onSessionEnd() {
	inputSourcesMap.forEach( function ( controller, inputSource ) {
	controller.disconnect( inputSource );
	} );