Make preloadFont callback optional

[crystalfp]

First, thanks for the library, it is really useful!
My application is ElectronJS + Vue + vite + Typescript.
I preload font glyphs but don't need to do anything at the end of the preload. So currently I do:

	preloadFont({
			font: localRoboto,
			characters: "ABC"
		},
		() => {}
	);

This works, but if I don't put the no-op callback, vite complains at runtime, even if I clean its cache:

Unhandled rejection TypeError: callback is not a function
    at http://localhost:5173/node_modules/.vite/deps/troika-three-text.js?v=30d82b0d:4648:7

Note that omitting the callback seems valid because preloadFont() calls getTextRenderInfo() that explicitly checks for callback defined and doesn't call it if not defined.
BTW, I typed the function in troika-three-text.d.ts as: declare function preloadFont(options: {font: string, characters: string}, callback?: () => void): void;

I don't understand if I'm doing something wrong or it is a feature to be added to Troika text.
Thanks!

[lojjic]

I guess I never considered a user would want to preload but not care about when the preload finishes. But sure, it makes sense to me!

calls getTextRenderInfo() that explicitly checks for callback defined and doesn't call it if not defined

I don't actually see that, it seems unconditional - I think that check just needs to be added.

[crystalfp]

I have seen this in file troika-three-text.esm.js line 3015.