WebVRManager: Reset camera rotation when not presenting.

src/renderers/webvr/WebVRManager.js

@@ -237,6 +237,8 @@ function WebVRManager( renderer ) {
 		if ( isPresenting() === false ) {
 
 			camera.position.set( 0, userHeight, 0 );
+			camera.rotation.set( 0, 0, 0 );
+
 			return camera;
 
 		}