Log warning message when failing to uninject from velocity initializer

It shouldn't break anything, but it's a massive memory leak

Follow-up to #1379

velocity/src/main/java/io/github/retrooper/packetevents/injector/VelocityPipelineInjector.java

@@ -82,9 +82,11 @@ public class VelocityPipelineInjector implements ChannelInjector {
         if (wrapper instanceof VelocityChannelInitializer) {
             try {
                 SET_SERVER_INTIIALIZER.invoke(initializerHolder, ((VelocityChannelInitializer) wrapper).getWrappedInitializer());
-            } catch (IllegalAccessException | InvocationTargetException e) {
-                e.printStackTrace();
+            } catch (IllegalAccessException | InvocationTargetException exception) {
+                throw new RuntimeException("Failed to uninject from frontend pipeline", exception);
             }
+        } else {
+            throw new IllegalStateException("Failed to uninject from frontend pipeline: can't unwrap foreign channel initializer");
         }
     }
 

velocity/src/main/java/io/github/retrooper/packetevents/velocity/factory/VelocityPacketEventsBuilder.java

@@ -234,8 +234,13 @@ public class VelocityPacketEventsBuilder {
             @Override
             public void terminate() {
                 if (initialized) {
-                    // Uninject the injector
-                    injector.uninject();
+                    // try to uninject the injector
+                    try {
+                        this.injector.uninject();
+                    } catch (Exception exception) {
+                        this.logManager.warn("Failed to uninject from initializer");
+                        exception.printStackTrace();
+                    }
                     // Remove handlers for players
                     for (User user : this.protocolManager.getUsers()) {
                         Channel channel = (Channel) user.getChannel();