Fix NPE race condition in ServerListPingEvent

Fixes GH-1473

If a ping is responded to prior to the server sample being populated
(pre-tick as an example) it can result in an NPE.

Spigot-Server-Patches/0240-Implement-extended-PaperServerListPingEvent.patch

@@ -91,7 +91,7 @@ index 0000000000..350410527b
 +
 +    private StandardPaperServerListPingEventImpl(MinecraftServer server, NetworkManager networkManager, ServerPing ping) {
 +        super(server, new PaperStatusClient(networkManager), ping.getServerData().getProtocolVersion(), server.server.getServerIcon());
-+        this.originalSample = ping.getPlayers().getSample();
++        this.originalSample = ping.getPlayers() == null ? null : ping.getPlayers().getSample(); // GH-1473 - pre-tick race condition NPE
 +    }
 +
 +    @Nonnull