Fix avatar page not loading

[netpro2k]

Avatar page fails to load because a roundabout dependency chain¹ ends up loading netcode.js, which expects NAF to exist. Untangling that is a bit difficult, but also we don't want to be using NAF in the new netcode anyway, so for now just add a check to prevent the page from failing to load.

The real fix is to continue removing use of globals like APP and NAF and to figure out a better solution for system initialization than directly executing code in the module.

Footnotes

1. avatar.js loads app.ts to define the APP global, since various things rely on it. app.ts needs mainTick from hubs-systems.ts which in turns ends up also loading all the systems code, including netcode.ts which immediately executes some code relying on NAF global. ↩