registerReloadListener called on wrong thread

Resource reload listeners should not be added in FMLClientSetupEvent or FMLCommonSetupEvent; these fire in parallel with vanilla actually triggering the resource reload, so doing this causes several issues:

• Your listener will potentially be ignored, if it gets added to the list after the reload starts.
• If you add the listener on the wrong thread (very likely when using the setup events) it will potentially cause a ConcurrentModificationException to happen later during the resource reload (e.g. https://github.com/embeddedt/ModernFix/issues/512), with no trace as to which mod caused the issue.

In general, you should not need to use the vanilla registerReloadListener method directly. Prefer using the platform-provided events for adding reload listeners. (Neo)Forge already provides RegisterClientReloadListenersEvent for clients, and AddReloadListenerEvent for servers.