Fix: Don't mistakingly assume that Geyser-Velocity initialized (#4276)

* Fix: ListenerBoundEvent could set `INITIALIZED` to true, even if we did not initialize yet - move that to postStartup() instead.

* only assign INITIALIZED once, and only after the correct listenertype bound.

bootstrap/velocity/src/main/java/org/geysermc/geyser/platform/velocity/GeyserVelocityPlugin.java

@@ -206,9 +206,9 @@ public class GeyserVelocityPlugin implements GeyserBootstrap {
                 // After this bound, we know that the channel initializer cannot change without it being ineffective for Velocity, too
                 geyserInjector.initializeLocalChannel(this);
             }
-        }
 
-        INITIALIZED = true;
+            INITIALIZED = true;
+        }
     }
 
     @Override