fix: set current stack to null when changing gui

fixes #7

src/main/java/dev/tilera/auracore/api/ICrystal.java

@@ -27,4 +27,6 @@ public interface ICrystal {
      */
     void harvestShard(EntityPlayer player);
 
+    boolean canHarvest(EntityPlayer player);
+
 }

src/main/java/dev/tilera/auracore/container/SlotWorkbenchWand.java

@@ -30,6 +30,7 @@ class SlotWorkbenchWand extends Slot {
             !this.workbench.getWorldObj().isRemote && 
             this.inventory.getStackInSlot(this.getSlotIndex()) != null &&
             this.inventory.getStackInSlot(this.getSlotIndex()).getItem() instanceof ItemWandCasting) {
+                player.inventory.setItemStack(null);
                 player.openGui(Thaumcraft.instance, 13, this.workbench.getWorldObj(), this.workbench.xCoord, this.workbench.yCoord, this.workbench.zCoord);
             }
     }

src/main/java/dev/tilera/auracore/mixins/MixinTileCrystal.java

@@ -119,4 +119,10 @@ public abstract class MixinTileCrystal extends TileThaumcraft implements ICrysta
         worldObj.spawnEntityInWorld(entity);
     }
 
+    @Override
+    public boolean canHarvest(EntityPlayer player) {
+        int md = this.worldObj.getBlockMetadata(this.xCoord, this.yCoord, this.zCoord);
+        return md != 6 && md != 9 && count > 1;
+    }
+
 }