[Pro] Thumbs breaks if custom image is provided but not found on server

[loltag22]

Considering the example from the official guide:

<FsLightbox
	sources={[
		"/Images/1.jpg",
		"/Images/2.jpg",
		"https://www.youtube.com/watch?v=3nQNiWdeH2Q",
		"/Videos/1.mp4"
	]}
	thumbs={[
		null, // The thumb will be created automatically.
		"/Images/Thumbs/2.jpg", // The default thumb is being overwritten.
		"/Images/Videos_Thumbs/1.jpg",
		"/Images/Videos_Thumbs/2.jpg"
	]}
/>

If for example "/Images/Thumbs/2.jpg" is not found on server, the loader over the thumbs section will never disappear.