Add code to prevent GUI staying open if chisel item is not in hand

src/main/java/com/cricketcraft/chisel/client/gui/GuiChisel.java

@@ -6,6 +6,7 @@ import net.minecraft.client.resources.I18n;
 import net.minecraft.entity.player.EntityPlayer;
 import net.minecraft.entity.player.InventoryPlayer;
 import net.minecraft.inventory.Slot;
+import net.minecraft.item.ItemStack;
 
 import org.lwjgl.opengl.GL11;
 
@@ -56,6 +57,15 @@ public class GuiChisel extends GuiContainer {
 		}
 	}
 
+	@Override
+	public void updateScreen() {
+		super.updateScreen();
+		ItemStack held = player.getCurrentEquippedItem();
+		if (held == null || !(held.getItem() instanceof IChiselItem)) {
+			mc.displayGuiScreen(null);
+		}
+	}
+
 	private void setButtonText() {
 		((GuiButton) buttonList.get(0)).displayString = I18n.format(container.inventory.getInventoryName() + ".mode." + currentMode.name().toLowerCase());
 	}