Fix mobs not spawning when using an older config (#9793)

patches/server/Paper-config-files.patch

@@ -4606,6 +4606,7 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 @@ -0,0 +0,0 @@
 +package io.papermc.paper.configuration.type.number;
 +
++import com.google.common.base.Preconditions;
 +import com.mojang.logging.LogUtils;
 +import java.util.OptionalInt;
 +import java.util.function.Function;
@@ -4669,7 +4670,8 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +
 +        @Override
 +        protected boolean belowZero(final OptionalInt value) {
-+            return false;
++            Preconditions.checkArgument(value.isPresent());
++            return value.getAsInt() < 0;
 +        }
 +
 +        @Override