Don't initalize activeModPack to an empty mod pack

Avoid possible use of an unintended empty mod pack by not setting the
activeModPack on the Instance until it's loaded in syncMods.  This was a
leftover from when a newly created empty mod pack was supposed to act as
the default when no mod pack was set.

packages/host/src/Instance.ts

@@ -108,7 +108,7 @@ export default class Instance extends lib.Link {
 	/**
 	 * Mod pack currently running on this instance
 	 */
-	activeModPack = new lib.ModPack();
+	activeModPack!: lib.ModPack; // This is set in syncMods
 	/**
 	 * Per player statistics recorded by this instance.
 	 */