Merge pull request 'Add Custom Callbacks for SWListInv' (#218) from hotfix_custom_callbacks into master

Reviewed-on: #218
Reviewed-by: YoyoNow <jwsteam@nidido.de>
Reviewed-by: Lixfel <lixfel@steamwar.de>

SpigotCore_Main/src/de/steamwar/inventory/SWListInv.java

@@ -28,6 +28,7 @@ import org.bukkit.entity.Player;
 import org.bukkit.event.inventory.ClickType;
 
 import java.util.*;
+import java.util.stream.Collectors;
 
 public class SWListInv<T> extends SWInventory {
 
@@ -55,8 +56,10 @@ public class SWListInv<T> extends SWInventory {
     public void open(){
         opened = true;
         inventory.clear();
-        callbacks.clear();
+        callbacks.keySet().stream().filter(i -> i >= 0).collect(Collectors.toList()).forEach(callbacks::remove);
-        setCallback(-999, (ClickType click) -> player.closeInventory());
+        if(!callbacks.containsKey(-999)) {
+            setCallback(-999, (ClickType click) -> player.closeInventory());
+        }
 
         if (sizeBiggerMax()) {
             if (page != 0) {