Display a game message if a cyclic error occurs

The message is displayed as a general message in the UI until the next
successful sort, giving users something to refer to if they try to fix
the issue.

Fixes #421.

src/gui/handler.cpp

@@ -953,7 +953,15 @@ namespace loot {
         }
         catch (loot::error& e) {
             BOOST_LOG_TRIVIAL(error) << "Failed to sort plugins. Details: " << e.what();
-            callback->Failure(e.code(), (boost::format(loc::translate("Failed to sort plugins. Details: %1%")) % e.what()).str());
+            if (e.code() == error::sorting_error) {
+                _lootState.CurrentGame().AppendMessage(Message(Message::error, e.what()));
+
+                YAML::Node node;
+                node["globalMessages"] = GetGeneralMessages();
+                callback->Success(JSON::stringify(node));
+            }
+            else
+                callback->Failure(e.code(), (boost::format(loc::translate("Failed to sort plugins. Details: %1%")) % e.what()).str());
         }
     }
 

src/gui/html/js/events.js

@@ -101,6 +101,11 @@ function onSortPlugins() {
 
     loot.game.globalMessages = result.globalMessages;
 
+    if (!result.plugins) {
+      loot.Dialog.closeProgress();
+      return;
+    }
+
     /* Check if sorted load order differs from current load order. */
     const loadOrderIsUnchanged = result.plugins.every((plugin, index) => {
       return plugin.name === loot.game.plugins[index].name;