Correctly reset status when context menu is closed

app/src/main/java/de/kuschku/quasseldroid/ui/chat/messages/MessageListFragment.kt

@@ -223,6 +223,9 @@ class MessageListFragment : ServiceBoundFragment() {
                 else              -> false
               }
             }
+            menu.setOnDismissListener {
+              linkMenu = null
+            }
             menu.show()
           }
         }