SPIGOT-7643: Fix inverted leash event cancelled usage and remove leash knot if no entity gets leashed

nms-patches/net/minecraft/world/item/ItemLeash.patch

@@ -30,7 +30,7 @@
          EntityLeash entityleash = null;
          double d0 = 7.0D;
          int i = blockposition.getX();
-@@ -54,12 +59,29 @@
+@@ -54,19 +59,50 @@
  
          EntityInsentient entityinsentient;
  
@@ -55,13 +55,23 @@
 +
 +            // CraftBukkit start
 +            if (org.bukkit.craftbukkit.event.CraftEventFactory.callPlayerLeashEntityEvent(entityinsentient, entityleash, entityhuman, enumhand).isCancelled()) {
-+                entityinsentient.setLeashedTo(entityleash, true);
++                iterator.remove();
++                continue;
 +            }
++
++            entityinsentient.setLeashedTo(entityleash, true);
 +            // CraftBukkit end
          }
  
          if (!list.isEmpty()) {
-@@ -69,4 +91,10 @@
+             world.gameEvent((Holder) GameEvent.BLOCK_ATTACH, blockposition, GameEvent.a.of((Entity) entityhuman));
+             return EnumInteractionResult.SUCCESS;
+         } else {
++            // CraftBukkit start- remove leash if we do not leash any entity because of the cancelled event
++            if (entityleash != null) {
++                entityleash.discard(null);
++            }
++            // CraftBukkit end
              return EnumInteractionResult.PASS;
          }
      }