Fix the case where the bookmark key is the same key that is used to close a GUI. (#433)

* This should fix the case where the bookmark key is the same key that is used to close a GUI

* Spotless

src/main/java/codechicken/nei/BookmarkContainerInfo.java

@@ -22,7 +22,10 @@ public class BookmarkContainerInfo {
     }
 
     public static IBookmarkContainerHandler getBookmarkContainerHandler(GuiContainer gui) {
-        return handlerMap.get(gui.getClass());
+        if (gui != null) {
+            return handlerMap.get(gui.getClass());
+        }
+        return null;
     }
 
     public static void load() {