Fix 1.17.1 -> 1.18 mappings loading (#676)

Closes https://github.com/ViaVersion/ViaBackwards/issues/568

common/src/main/java/com/viaversion/viabackwards/protocol/protocol1_17_1to1_18/data/BackwardsMappings.java

@@ -33,6 +33,8 @@ public final class BackwardsMappings extends com.viaversion.viabackwards.api.dat
 
     @Override
     protected void loadExtras(final CompoundTag data) {
+        super.loadExtras(data);
+
         for (final Object2IntMap.Entry<String> entry : Protocol1_18To1_17_1.MAPPINGS.blockEntityIds().object2IntEntrySet()) {
             blockEntities.put(entry.getIntValue(), entry.getKey());
         }