fix: check if app.renderer is not null before calling destroy()

[Yovach]

When destroy() is called, Pixi.js sets renderer to null (see the source at https://github.com/pixijs/pixijs/blob/f60121308acbba32f81333a7918c3a4998172885/src/app/Application.ts#L416).

Because React.StrictMode may invoke the "unmount" helper twice during development, this can results in a crash.

[Yovach]

I attempted to call destroy(true, true), but that caused a crash. This pull request should resolve the problem: pixijs/pixijs#11659

Calling destroy() with no arguments triggers glitches beginning on the third refresh.