reset the actMode on destroy

app/src/main/kotlin/com/simplemobiletools/filemanager/adapters/ItemsAdapter.kt

@@ -97,6 +97,7 @@ class ItemsAdapter(val activity: SimpleActivity, var mItems: MutableList<FileDir
             super.onDestroyActionMode(actionMode)
             views.forEach { toggleItemSelection(it, false) }
             markedItems.clear()
+            actMode = null
         }
     }