Fix tap unit if destroyShield returns false

public/board.js

@@ -995,7 +995,9 @@ class Board{
 			case 'shield':
 				// If the shield is tapped 'destroy' it
 				if(this.isTapped(itemDefending)){
-					this.destroyShield(itemDefending);
+					if(!this.destroyShield(itemDefending)){
+						break;	
+					}
 				}
 				// Otherwise tap the shield, so it can be destroyed in future
 				else{