Results 6 issues of Platane

hello, Due to `typeof null === 'object` the isPromise test is crashing when passing `null` Here a demo: https://codesandbox.io/s/3vyq17zy35 This PR fix that

Hi :wave: Thanks for this project, I find it pretty useful :) I made some changes to allow to drop multiple files ( gltf file + textures and binaries as...

~~[267](https://user-images.githubusercontent.com/1659820/117716664-2663e580-b1da-11eb-971c-eb241c4297bf.jpg)~~ ~~[271](https://user-images.githubusercontent.com/1659820/107849275-778e5400-6dfa-11eb-85ef-bdfdf4635885.png)~~ [292](https://user-images.githubusercontent.com/1659820/233065309-a39855e7-c044-4da9-837b-d57e04b5367e.png)