Fix custom sound handling in 1.9->1.8 (#691)

Author: Beaness

common/src/main/java/com/viaversion/viarewind/protocol/v1_9to1_8/rewriter/WorldPacketRewriter1_9.java

@@ -92,9 +92,12 @@ public void register() {
                     String name = wrapper.get(Types.STRING, 0);
                     name = protocol.getMappingData().getMappedNamedSound(name);
                     if (name == null) {
-                        wrapper.cancel();
-                    } else {
+                        return;
+                    }
+                    if (!name.isEmpty()) {
                         wrapper.set(Types.STRING, 0, name);
+                    } else {
+                        wrapper.cancel();
                     }
                 });
                 read(Types.VAR_INT); // Sound category