Clear message queue when destroying GUIEngine

So it won't call font which could already been reset

src/guiengine/engine.cpp

@@ -834,6 +834,7 @@ namespace GUIEngine
         needsUpdate.clearWithoutDeleting();
 
         gui_messages.clear();
+        MessageQueue::clear();
     }   // clear
 
     // ------------------------------------------------------------------------

src/guiengine/message_queue.cpp

@@ -384,6 +384,23 @@ void showProgressBar(int progress, const core::stringw& msg)
 #endif
 }   // showProgressBar
 
+// ----------------------------------------------------------------------------
+/** Clear all message, called when destroying the GUIEngine.
+ */
+void clear()
+{
+#ifndef SERVER_ONLY
+    g_all_messages.lock();
+    while (!g_all_messages.getData().empty())
+    {
+        Message* msg = g_all_messages.getData().top();
+        delete msg;
+        g_all_messages.getData().pop();
+    }
+    g_all_messages.unlock();
+#endif
+}
+
 }   // namespace GUIEngine
 
 // ----------------------------------------------------------------------------

src/guiengine/message_queue.hpp

@@ -47,6 +47,6 @@ namespace MessageQueue
     void showProgressBar(int progress, const core::stringw& msg);
     void updatePosition();
     void update(float dt);
-
+    void clear();
 };   // namespace GUIEngine
 #endif