Fix camera event handler staying registered leading to lack of HUD

When unloading the camera without killing it first (e.g. jumping back
in time), the event handler wouldn't ever get unregistered.

src/main/java/com/replaymod/replay/camera/CameraEntity.java

@@ -116,7 +116,7 @@ public class CameraEntity
      * Therefore we cannot register any event handlers directly in the CameraEntity class and
      * instead have this inner class.
      */
-    private final EventHandler eventHandler = new EventHandler();
+    private EventHandler eventHandler = new EventHandler();
 
     public CameraEntity(
             MinecraftClient mcIn,
@@ -525,10 +525,22 @@ public class CameraEntity
     @Override
     public void remove() {
         super.remove();
-        eventHandler.unregister();
+        if (eventHandler != null) {
+            eventHandler.unregister();
+            eventHandler = null;
+        }
     }
 
     private void update() {
+        MinecraftClient mc = MinecraftClient.getInstance();
+        if (mc.world != this.world) {
+            if (eventHandler != null) {
+                eventHandler.unregister();
+                eventHandler = null;
+            }
+            return;
+        }
+
         long now = System.currentTimeMillis();
         long timePassed = now - lastControllerUpdate;
         cameraController.update(timePassed / 50f);