fix(rcon): upsert offline pixel grants

RCON GivePixels previously used an UPDATE for offline users, so users without an existing users_currency type 0 row received no pixels while the command still returned success. Match the GivePoints and housekeeping paths with an upsert and add a contract test that keeps offline pixel grants creating missing currency rows.

Emulator/src/main/java/com/eu/habbo/messages/rcon/GivePixels.java

@@ -26,10 +26,11 @@ public class GivePixels extends RCONMessage<GivePixels.JSONGivePixels> {
         if (habbo != null) {
             habbo.givePixels(object.pixels);
         } else {
-            try (Connection connection = Emulator.getDatabase().getDataSource().getConnection(); PreparedStatement statement = connection.prepareStatement("UPDATE users_currency SET users_currency.amount = users_currency.amount + ? WHERE users_currency.user_id = ? AND users_currency.type = 0")) {
-                statement.setInt(1, object.pixels);
-                statement.setInt(2, object.user_id);
-                statement.execute();
+            try (Connection connection = Emulator.getDatabase().getDataSource().getConnection(); PreparedStatement statement = connection.prepareStatement("INSERT INTO users_currency (`user_id`, `type`, `amount`) VALUES (?, 0, ?) ON DUPLICATE KEY UPDATE amount = amount + ?")) {
+                statement.setInt(1, object.user_id);
+                statement.setInt(2, object.pixels);
+                statement.setInt(3, object.pixels);
+                statement.executeUpdate();
             } catch (SQLException e) {
                 this.status = RCONMessage.SYSTEM_ERROR;
                 LOGGER.error("Caught SQL exception", e);

Emulator/src/test/java/com/eu/habbo/messages/rcon/GivePixelsContractTest.java

@@ -0,0 +1,24 @@
+package com.eu.habbo.messages.rcon;
+
+import org.junit.jupiter.api.Test;
+
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class GivePixelsContractTest {
+    private static String givePixelsSource() throws Exception {
+        return Files.readString(Path.of("src/main/java/com/eu/habbo/messages/rcon/GivePixels.java"));
+    }
+
+    @Test
+    void offlinePixelGrantCreatesMissingCurrencyRow() throws Exception {
+        String source = givePixelsSource();
+
+        assertTrue(source.contains("INSERT INTO users_currency"),
+                "Offline RCON pixel grants must create the users_currency type 0 row when it is missing");
+        assertTrue(source.contains("ON DUPLICATE KEY UPDATE"),
+                "Offline RCON pixel grants should increment existing rows with an upsert");
+    }
+}