Fix Bukkit data not being loaded while offline

Closes #16

internal/v1_16_R3/src/main/java/com/lishid/openinv/internal/v1_16_R3/OpenPlayer.java

@@ -32,15 +32,24 @@ public class OpenPlayer extends CraftPlayer {
         super(server, entity);
     }
 
+    @Override
+    public void loadData() {
+        // See CraftPlayer#loadData
+        NBTTagCompound loaded = this.server.getHandle().playerFileData.load(this.getHandle());
+        if (loaded != null) {
+            readExtraData(loaded);
+        }
+    }
+
     @Override
     public void saveData() {
-        super.saveData();
         EntityPlayer player = this.getHandle();
         // See net.minecraft.server.WorldNBTStorage#save(EntityPlayer)
         try {
             WorldNBTStorage worldNBTStorage = player.server.getPlayerList().playerFileData;
 
             NBTTagCompound playerData = player.save(new NBTTagCompound());
+            setExtraData(playerData);
 
             if (!isOnline()) {
                 // Special case: save old vehicle data

internal/v1_16_R3/src/main/java/com/lishid/openinv/internal/v1_16_R3/PlayerDataManager.java

@@ -57,8 +57,7 @@ public class PlayerDataManager implements IPlayerDataManager {
         }
     }
 
-    @NotNull
-    public static EntityPlayer getHandle(final Player player) {
+    public static @NotNull EntityPlayer getHandle(final Player player) {
         if (player instanceof CraftPlayer) {
             return ((CraftPlayer) player).getHandle();
         }
@@ -78,9 +77,8 @@ public class PlayerDataManager implements IPlayerDataManager {
         return nmsPlayer;
     }
 
-    @Nullable
     @Override
-    public Player loadPlayer(@NotNull final OfflinePlayer offline) {
+    public @Nullable Player loadPlayer(@NotNull final OfflinePlayer offline) {
         // Ensure player has data
         if (!offline.hasPlayedBefore()) {
             return null;